Complete JavaScript Localization Guide: From Setup to Production

When you initially develop an application, internationalization of that app or website doesn’t come to mind. Eventually, however, you discover a substantial untapped audience blocked by the language barrier. Consider that there are people who only understand their native language and originate from different countries, such as Poland, England, the USA, and Mexico, who are accessing your App or Website. How will they understand the services or products you are offering? Here, JavaScript Localization comes into the picture.

Let me tell you why we need it.

According to statistics, more than 76% of online buyers prefer to purchase a product if the description is in their native language. At the same time, 40% of them do not prefer to buy from websites only in English.

JavaScript localization is one of the most effective ways to adapt your entire application into a language users can easily understand.

What you will master from this guide:

• What is JavaScript Localization, and why use it?
• Comprehensive knowledge of JavaScript Localization and its Implementation.
• Perfect tool selection and workflow optimization.
• We’ll walk through some of the best JS Localization tools, including i18next, FormatJS, and more..
• An advanced tool integration with Crowdin
• Get the best production-ready practices.

Understanding the Fundamentals

Let’s dive in and start understanding JS Localization in detail:

JavaScript has been one of the most widely used and popular programming languages for over a decade for creating web, mobile, and desktop applications. Not only that, it’s also used in building some more data-centric and real-time data-intensive applications. According to W3Techs, more than 98.9% of the websites on the frontend use JavaScript.

What is JavaScript Localization?

JavaScript localization is the process of building applications that support multiple native languages for different regions and countries. With localization, users experience the entire application in their native language, which encompasses translated text, date and time formatting, currency changes, text direction support (for RTL for Arabic Nations), and many other features.

Building an application aiming at a global audience makes localization essential, not an optional feature. Almost every tech giant, such as Facebook, Google, and Amazon, uses robust localization mechanisms built for their apps to serve their audience worldwide.

Two standards that are important for developers to localize their applications. We have to follow them in order:

Internationalization (i18n) - It ensures that the application is ready to localize for different languages or regions. This i18n is used for separating the presentation layer from business logic to support a multi-locale localization workflow.

Localization (l10n) - Localization takes that whole internationalization-specific code or architecture, and then adapts it for a specific country or region. Here, locale-specific formatting takes place.

You can add files for each locale as follows:

• en-US.json, - for USA
• fr-FR.json, - for France
• ja-JP.json, - for Japan

Each file will contain the right words and settings for the architecture developed for localization. Learn more about i18n vs l10n in detail.

Locale - Locale is something that distinguishes not only the language but also cultural conventions, such as measurements, used in specific regions. We define the locales in .json files to ensure accessibility in any environment, so they’re environment-agnostic and reusable.

Difference Between JavaScript Localization and JavaScript Translation

JavaScript translation is limited to converting text. It focuses only on words, messages, and phrases visible to users, without addressing region-specific adaptation.

JavaScript localization was discussed in detail earlier. Here is the table differentiating between JavaScript Translation and Localization:

Why Localization Matters

The localization market is already large and getting bigger: from $6.27B in 2025 to about $19.18B by 2035 - roughly 11.8% growth each year.

One more thing is there – if you provide a localized feel to a product, then there is a big opportunity to sell it because their cultural context matches their vibe.

A few key components to keep in mind before adapting localization:

1. Pick one market where you see some initial traffic and potential
2. What is the first thing to localize - I would say currency and taxes, and checkout options for better flexibility to the users.
3. Keep your brand tone intact across all the regions.

User Experience Improvements - Recent metrics show that localized applications have more engagement:

• Users spend more than 40% more time on websites that are in their native language.
• Another report says that more than 65% of e-commerce users are more likely to buy their stuff from native language-based websites.

SEO Benefits - Multilingual websites have a few key advantages:

• They rank higher in local native searches and assure the user’s intent.
• User intent-based search is now a factor in all search engines like Google, Bing, and DuckDuckGo.

Competitive Advantage:

• Companies that adopt localization have demonstrated significantly better growth rates and a first-mover advantage, capturing 30-40% of the market.
• Manual localization is a nightmare for developers because you have to manage scattered text. Initially, it looks easy, but when your app grows, the text that you had earlier will also grow enormously and sometimes become unmanageable.

Here, I’m going to cover a couple of points, and these will help you understand why you should go with the automation way of doing localization instead of manual localization.

Challenges of Doing Localization Manually:

1. The Hardcoded String Makes Application Maintenance Hard

Here are the major issues that initially don’t feel like a problem unless your application goes enormously big!

• Code duplication - impacts on translations.
• Every time a new locale is added, it increases the deployment issues.

2. Context Loss = Poor Translations

• Region to region, the meaning of the same word changes.
• Polysemy makes the translation more complex, incorrect, and inconsistent.

3. Version Control

• Merge conflicts occur when multiple locale-specific files are pushed concurrently.
• Merging branches creates multiple language divergences, yet another issue for developers.

4. Manual Extraction Wastes Dev Time

• Resource allocation - allocating developers to a non-core development task wastes their time.
• Manual language-specific data extraction breaks development workflows.

5. Inefficient Communication Gaps

• Sharing translation-related files via email/Slack doesn’t help in keeping the record.
• Tracking is nearly impossible. Figuring out what is done or pending is another problem.
• People might work on different file versions.

6. Integration Errors, Delays & QA Bottlenecks

• Manual syncing often means missing or inconsistent translations until late in testing.
• Easy to miss a few parts in the app for translation.
• Manually checking every translation across multiple languages is overwhelming.
• Testing complexity grows as more languages are added.
• Bad translation can lead to delays in product launch or the sending of updates.

JavaScript Localization Project Setup

Before directly moving towards the system and setup, let’s do some planning for the multilingual architecture of the application. We need to identify the target locales, business goals, conversion potential, UI elements, technical requirements, and a couple of other things. Let’s understand these things in detail:

Strategic Foundation: Checklist

Target Locales

• Research about the target countries where your application is used the most.
• Know your competitors and see what languages they are supporting.
• Target revenue and user engagement in specific markets, and always keep in mind:
• User Engagement, Conversion Potential, and Expected Revenue.

Audit Content

• Make a list of all the user-facing elements (buttons, menus, CTAs).
• Spot the content that requires cultural adaptation, like text embedding, or region-specific formatting (dates, currency conversions, measurements, etc.)

Technical Requirements

• Check if there are any existing internationalization libraries used in the project.
• Audit the codebase to check for hardcoded locale-based logic that might cause issues later.
• Database Schema Review
• APIs should be adaptable to accept language headers and locale-based routing.
• Bundling strategy to split the code based on locale (fr.chunk.js)
• Configure the CDN for handling locale-specific assets to improve performance.
• Subdomain approach to assign the locale-based content (yoursite.com/en, yoursite.com/fr, yoursite.com/jp)

Timeline and Resources Required

• Make a proper estimation for development ( coding + translation )
• Buffer time for unexpected issues.
• Plan testing for every language that you implement
• Avoid repetitive tasks by using automation tools.
• For better translation, work with native speakers.

Project Structure Best Practices

Here is the file structure that I would like to suggest to you. You can use this for future reference. The goal is to make a clear locale file structure as we do for business logic or project components.

Key Points to Consider:

• Organize locale files into a separate folder. Inside the folder, split the file according to the element structure of your project. Code, translations, and configuration.
• Clear folder structures to make the collaboration process easier between developers and translators.
• Avoid mixing translation logic with business code.

Folder Structure

src/
├── locales/
│   ├── en/
│   │   ├── common.json
│   │   ├── navigation.json
│   │   ├── forms.json
│   │   └── errors.json
│   ├── es/
│   │   ├── common.json
│   │   ├── navigation.json
│   │   └── forms.json
│   ├── fr/
│   └── de/
├── utils/
│   └── i18n.js
├── components/
└── hooks/
    └── useTranslation.js

Before & After Code Examples

The best way to get an understanding of internationalization is from the hardcoded translation to a properly implemented localization. We have shared a comparison by showing a small React component code where we demonstrate how the hardcoded string dynamic, localized, scalable component. Check out the second localization-ready code and how we have implemented the localization inside the component:

Problematic Hardcoded Approach

// ❌ Before: Hardcoded strings create maintenance nightmares
const WelcomeComponent = () => {
  return (
    <div>
      <h1>Welcome to our amazing app!</h1>
      <p>Please select your preferred language from the menu above.</p>
      <button>Get Started Now</button>
    </div>
  );
};

Localization-Ready Implementation

Here we are using the useTranslation hook from the React i18next library to translate any component props that are coming to the component.

// ✅ After: Structured, maintainable localization
import { useTranslation } from "react-i18next";

const WelcomeComponent = () => {
  const { t } = useTranslation("common");

  return (
    <div>
      <h1>{t("welcome.title")}</h1>
      <p>{t("welcome.description")}</p>
      <button>{t("actions.getStarted")}</button>
    </div>
  );
};

Corresponding Translation File Structure

This is the structure for sending data to the component from this particular JSON file. From this data, the component will understand what the title description and the action would be. And it will be presented in a localized manner in the component.

{
  "welcome": {
    "title": "Welcome to our amazing app!",
    "description": "Please select your preferred language from the menu above."
  },
  "actions": {
    "getStarted": "Get Started Now"
  }
}

Essential JavaScript i18n Libraries Comparison

The JS ecosystem offers many libraries for internationalization and localization that have their pros and cons, and we have to decide which one is best for our project requirements. Understanding of these libraries helps in making decisions for the best-suited library to use that meets long-term project goals as well as best project architecture.

Lingui: Developer Experience Champion

Lingui is a localization framework for JavaScript projects. It is framework-agnostic and can be used with technologies such as React, Next.js, Vue, and Svelte.

Key features of Lingui:

• Size and Performance: The core library is less than 2KB gzipped, and with React components, it’s an additional 1.4KB gzipped. It is designed to be lightweight, and developers can load only the necessary messages for the active language.
• Clean and Readable Code: Lingui offers a direct way to manage translations within the codebase, which can contribute to cleaner and more maintainable code.
• ICU Message Format Support: It supports the International Components for Unicode (ICU) Message Format, a standard for handling complex grammatical rules like plurals, genders, and ordinals.
• Rich-Text Support: The library provides support for rich-text, allowing for the inclusion of components and HTML tags within translated strings.
• AI-Friendly Localization: The localization formats used by Lingui can include context for strings, which can be used to improve the accuracy of machine and AI-assisted translations.
• Active Community: Developers can find support and ask questions on the project’s Discord and Stack Overflow channels.

Macro-powered development experience

import { useState, useEffect } from "react";
import { I18nProvider, Trans } from "@lingui/react";
import { i18n, dynamicActivate, defaultLocale } from "./config/i18n";
import LanguageSwitcher from "./components/LanguageSwitcher";
import "./App.css";

function App() {
  const [locale, setLocale] = useState(defaultLocale);
  useEffect(() => {
    dynamicActivate(locale);
  }, [locale]);

  // Handle language switching
  const handleLocaleChange = (newLocale) => {
    setLocale(newLocale);
    dynamicActivate(newLocale);
  };

  const user = { name: "Ben Robins" };

  return (
    // i18n provider wraps: To provide translation context
    <I18nProvider i18n={i18n}>
      <div className="App">
        <header className="App-header">
          {/* Language selector */}
          <LanguageSwitcher currentLocale={locale} onLocaleChange={handleLocaleChange} />

          {/* Main Code Area */}
          <div>
            <div>
              <h1>
                <Trans id="greeting" values={{ 0: user.name }}>
                  Hey, {user.name}!
                </Trans>
              </h1>
              <p>
                <Trans id="motivational.message">
                  Right now, the technological space is changing a lot, and we are seeing more
                  demand for AI stuff. There are so many things that are right now being done by
                  artificial intelligence using ChatGPT, Claude, Gemini, and other LLMs. But still,
                  there are human needs that we can utilize all of them to make something better.
                  Let's build something great.
                </Trans>
              </p>
            </div>
          </div>
        </header>
      </div>
    </I18nProvider>
  );
}

export default App;

i18next: The Most Commonly Used Solution

With over 8.8 million weekly downloads and 8.2K stars on GitHub, it is one of the best libraries with enormous functionalities. i18next is one library that I can recommend for smaller to bigger enterprise-level applications.

Key Features of i18next:

• i18next is versatile, and it offers architecture support to vanilla JavaScript, React, Vue, Next.js, Angular, and Node.js environments seamlessly.
• It offers an ecosystem through which you can add plugins made on top of it and add additional features as per your needs.
• Namespace organization capabilities - this is used for logic-based separation of translations, components, or application sections.
• For complex interpolation, it uses translation function chaining and context-dependent translations.

i18next Implementation Example

import i18n from "i18next";
import { initReactI18next } from "react-i18next";
import HttpBackend from "i18next-http-backend";

i18n
  .use(HttpBackend) // Load translations from server
  .use(initReactI18next) // Pass i18n down to react-i18next
  .init({
    lng: "en",
    fallbackLng: "en",
    debug: process.env.NODE_ENV === "development",

    interpolation: {
      escapeValue: false // React already escapes
    },

    backend: {
      loadPath: "/locales/{{lng}}/{{ns}}.json"
    },

    // Namespace configuration
    ns: ["common", "navigation", "forms"],
    defaultNS: "common"
  });

export default i18n;

FormatJS: React’s Powerhouse

Another arsenal, and this is for React.js. With over 1.7 million weekly downloads, it is one of the most popular libraries for internationalization. It is one of the best fits for the React ecosystem and one of the most advanced libraries that supports pluralization, date/time formatting, and more.

Key Features of FormatJS:

• Date, Number, String Formatting
• Extraction and Translation Management
• ICU Message Support - includes pluralization, gender, and other rules
• Rich text and Nested Formatting are also supported
• JSON Management
• Integration with Modern techs like React, Next.js, React Native

Advanced Formatting Capabilities:

import { FormattedMessage, FormattedNumber, FormattedDate } from "react-intl";

const ProductCard = ({ product, user }) => (
  <div>
    <FormattedMessage
      id="product.welcome"
      defaultMessage="Hello {name}, you have {itemCount, plural, one {# item} other {# items}} in your cart"
      values={{
        name: user.name,
        itemCount: product.quantity
      }}
    />

    <FormattedNumber value={product.price} style="currency" currency="USD" />

    <FormattedDate value={product.availableDate} year="numeric" month="long" day="2-digit" />
  </div>
);

Selection Criteria Framework

It is very important to select a particular internationalization library. Here I am going to share a couple of criteria to evaluate any library and check if it aligns with your project and team capabilities.

• Project Size and Complexity: Enterprise-level applications benefit from i18next’s enormous feature set and the plugin ecosystem. The smaller projects can utilize one of the robust and most performing libraries, Lingui. Small, yet powerful, and supports almost all features.
• Framework Compatibility: React projects gain significant advantages from FormatJS’s specialized React integration, while Vue applications naturally benefit from Vue i18n’s template-first approach.
• Team Expertise Level: Teams new to internationalization often find Lingui’s macro approach more intuitive, while experienced developers appreciate i18next’s flexibility and power.
• Performance Requirements: Applications prioritizing minimal bundle sizes benefit from LinguiJS’s 2KB footprint, while projects needing extensive formatting capabilities justify FormatJS’s larger bundle.
• Long-term Maintenance Considerations: i18next’s mature ecosystem and comprehensive documentation support long-term maintenance, while framework-specific solutions may offer better integration but potentially longer migration paths.

Localization Implementation Methods & Advanced Techniques

Now we are going to see some code samples that will walk you through how things work in particular frameworks or vanilla JavaScript. How you can utilize native APIs, other libraries like i18next and LinguiJS, as we have discussed earlier in the document.

We have discussed multiple libraries earlier; one more option that we can use for localization, the browser’s native API. With Native APIs, we can utilize the browser’s built-in API that supports internationalization and convert the language according to the user’s region.

Leverage the Intl Object

Right now, the browsers are getting smarter every passing day. All modern browsers support internationalization via the Intl namespace. Intl, an in-built namespace offered in JavaScript. It works well with Browsers that are updated after 2017. So, if you are on the latest version of any browser (whether it is Safari, Chrome, or Mozilla), it will give you the best results.

Core Features That You Will Get with Intl Objects

• Built-in internationalization support
  • Internationalizing numbers
  • Date/time, currency
  • Pluralization
  • String comparison and more.
• Browser Integration - It uses locale data that is inside the browser for standard formatting.
• Unicode Support
• Native to JS, so there is no dependency required to add this to your website or app.

Here are some code samples that show how it works:

1. Number & Currency Formatting Using Intl

const formatCurrency = (amount, locale, currency) => {
  return new Intl.NumberFormat(locale, {
    style: "currency",
    currency: currency,
    minimumFractionDigits: 2,
    maximumFractionDigits: 2
  }).format(amount);
};

console.log(formatCurrency(7564.56, "en-US", "USD"));
console.log(formatCurrency(7564.56, "de-DE", "EUR"));
console.log(formatCurrency(7564.56, "ja-JP", "JPY"));

// Unit formatting & pluralization
const distanceCalc = new Intl.NumberFormat("en-US", {
  style: "unit",
  unit: "kilometer",
  unitDisplay: "long"
});

console.log(distanceCalc.format(1.5)); // "1.5 kilometers"

2. Date and Time Localization Using Intl

const formatDate = (date, locale, options = {}) => {
  const defaultOptions = {
    year: "numeric",
    month: "long",
    day: "numeric",
    weekday: "long"
  };

  return new Intl.DateTimeFormat(locale, { ...defaultOptions, ...options }).format(date);
};

const now = new Date();

console.log(formatDate(now, "en-US"));
console.log(formatDate(now, "fr-FR"));
console.log(formatDate(now, "ja-JP"));

const rtf = new Intl.RelativeTimeFormat("en-US", {
  numeric: "auto",
  style: "long"
});

console.log(rtf.format(-1, "day"));
console.log(rtf.format(2, "hour"));
console.log(rtf.format(-3, "month"));

‘Intl Namespace’ is supported by more than 98% browsers and has global coverage. For legacy browsers, we can use intl-polyfills with FormatJS. With Polyfills, we can provide a consistent behavior of ‘Intl’ across all environments.

Framework-Specific Integration

The localization principle for all the technologies and frameworks is fundamentally the same. But every technology is approached with its own set of tools. Leveraging framework-specific libraries helps developers make more performant, manageable, and developer-friendly apps. Here are a couple of examples to go through:

React with react-i18next

React apps benefit from the react-i18next library. Its hook-based library and the architecture and Suspense integration are optimal for user experiences:

import { Suspense } from "react";
import { useTranslation } from "react-i18next";

function App() {
  const { t } = useTranslation("common");

  function UserProfile() {
    const { t, i18n } = useTranslation("profile");

    const user = {
      username: "Sam",
      description: "AI-focused full-stack developer."
    };

    const toggleLanguage = () => {
      i18n.changeLanguage(i18n.language === "en" ? "es" : "en");
    };

    return (
      <div className="user-profile">
        <div className="language-toggle">
          <button onClick={toggleLanguage}>
            {t("switchLanguage")} ({i18n.language === "en" ? "Español" : "English"})
          </button>
        </div>

        <div className="profile-card">
          <div className="profile-avatar">
            <span>{user.username.charAt(0).toUpperCase()} </span>
          </div>

          <h1>{t("title")}</h1>

          <div className="profile-info">
            <div className="username-section">
              <label>{t("username")}:</label>
              <span className="username">{user.username}</span>
            </div>

            <div className="description-section">
              <label>{t("description")}:</label>
              <p className="description">{t("userDescription")}</p>
            </div>
          </div>

          <div className="profile-footer">
            <small>
              {t("currentLanguage")}: {i18n.language.toUpperCase()}
            </small>
          </div>
        </div>
      </div>
    );
  }

  return (
    <Suspense fallback={<div className="loading">{t("loading")}</div>}>
      <div className="app">
        <UserProfile />
      </div>
    </Suspense>
  );
}

export default App;

Vue.js Implementation

Vue 3 has its own Composition API for Internationalization. With the help of this API, you can change the languages without even reloading the page. Not only that, but it also offers language settings to the entire application. In the earlier versions of Vue, we had to write more code, but now this one is coming up with a better organization and clear separation of the code files.

import { useI18n } from "vue-i18n";
import { computed, watch } from "vue";

export default {
  setup() {
    const { t, locale, availableLocales } = useI18n();

    // Reactive locale switching with persistence
    const currentLocale = computed({
      get: () => locale.value,
      set: (newLocale) => {
        locale.value = newLocale;
        localStorage.setItem("preferred-locale", newLocale);
        document.documentElement.lang = newLocale;
        document.documentElement.dir = getTextDirection(newLocale);
      }
    });

    // Automatic RTL detection
    const getTextDirection = (lang) => {
      const rtlLanguages = ["ar", "he", "fa", "ur"];
      return rtlLanguages.includes(lang.split("-")) ? "rtl" : "ltr";
    };

    // Watch for locale changes
    watch(locale, (newLocale) => {
      updatePageMeta();
    });

    const updatePageMeta = () => {
      // Update page metadata for SEO
      document.title = t("meta.title");
      const description = document.querySelector('meta[name="description"]');
      if (description) {
        description.setAttribute("content", t("meta.description"));
      }
    };

    return {
      t,
      currentLocale,
      availableLocales
    };
  }
};

Next.js Built-in Internationalization

Next.js provides sophisticated internationalization, routing, and server-side rendering support that optimizes SEO and initial page load performance:

import { NextResponse } from "next/server";
import { match } from "@formatjs/intl-localematcher";
import Negotiator from "negotiator";

const locales = ["en", "es"];
const defaultLocale = "en";

function getLocale(request) {
  const header = request.headers.get("Accept-Language") ?? undefined;
  const headers = { "accept-language": header };
  const languages = new Negotiator({ headers }).languages();
  return match(languages, locales, defaultLocale);
}

export function middleware(request) {
  const pathname = request.nextUrl.pathname;
  const missingLocale = locales.every(
    (locale) => !pathname.startsWith(`/${locale}/`) && pathname !== `/${locale}`
  );
  if (missingLocale) {
    const locale = getLocale(request);
    return NextResponse.redirect(new URL(`/${locale}${pathname}`, request.url));
  }
}

export const config = {
  matcher: ["/((?!_next|.*\\..*).*)"]
};

Dictionary Loader:

import en from "./dictionaries/en";
import es from "./dictionaries/es";

const dictionaries = {
  en: en,
  es: es
};

export async function getDictionary(locale) {
  return (dictionaries[locale] || dictionaries.en)();
}

English translations:

const en = () => ({
  name: "User",
  userName: "Sam",
  description: "AI-focused full-stack developer."
});

export default en;

Spanish translations:

const es = () => ({
  name: "Usuario",
  userName: "Sam",
  description: "Desarrollador full-stack centrado en IA."
});

export default es;

Language Switcher Component:

"use client";

import { useRouter, usePathname } from "next/navigation";

// Language Switcher Component
export function LanguageSwitcher({ currentLang }) {
  const router = useRouter();
  const pathname = usePathname();

  const languages = [
    { code: "en", name: "English", flag: "🇺🇸" },
    { code: "es", name: "Español", flag: "🇪🇸" }
  ];

  const switchLanguage = (newLang) => {
    // Correctly constructs the new path for Next.js app router.
    // Assumes the language code is the first segment after the domain.
    const segments = pathname.split("/");
    // This part is the most critical fix.
    // It creates a new path by replacing the language segment.
    const newPath = `/${newLang}${segments.slice(2).join("/")}`;
    router.push(newPath);
  };

  return (
    <>
      <span style={{ fontWeight: "bold" }}>Language:</span>
      {languages.map((lang) => (
        <button key={lang.code} onClick={() => switchLanguage(lang.code)}>
          <span>{lang.flag}</span>
          {lang.name}
        </button>
      ))}
    </>
  );
}

Layout Component:

import { Layout } from "@/components";

export default function RootLayout({ children, params }) {
  return <Layout lang={params.lang}>{children}</Layout>;
}

Page Component:

import { getDictionary } from "@/lib/dictionaries";
import { LanguageSwitcher, ProfileCard } from "@/components";

export default async function Home({ params }) {
  const { lang } = params;
  const dict = await getDictionary(lang);
  return (
    <div>
      <LanguageSwitcher currentLang={lang} />
      <ProfileCard dict={dict} lang={lang} />
    </div>
  );
}

How AI is transforming JavaScript Localization?

While AI is booming, here is the solution that provides AI-powered JavaScript localization. Utilization of such tools can help you localize your content faster than ever. Let me introduce you to one of the industry leaders in AI-powered localization - Crowdin.

Crowdin: Developer-Focused AI-Powered Localization Platform

Crowdin is one of the top platforms that offers AI-powered localization. Crowdin enables devs and business owners who want their apps, websites, games, and documents to be multilingual. It provides AI-supported automation.

With over 100K+ projects worldwide and over 3 million registered users, Crowdin becomes the first choice. Crowdin supports more than 100 file formats and 700+ app integrations that include HubSpot, GitHub, GitLab, Figma, and many others.

Crowdin facilitates multilingual operations of enterprise-level applications like Microsoft, GitHub, GitLab, etc.

Key Features of Crowdin:

• Cloud-Based SaaS
• AI
• Integration Libraries
• Continuous Localization
• Advanced Localization and Translation Management Tools
• High-Security Standards
• GitHub/GitLab/BitBucket Integration

How to Use Crowdin to Localize a JS App Using Crowdin CLI?

Crowdin CLI is the best and well-organized tool for handling translation downloads, file uploads without any APIs. Crowdin offers APIs as well, but CLI is more streamlined, and because it’s a command line, localization workflows and environment setup become easier for developers.

What is Crowdin CLI?

Crowdin CLI is a tool that works in the command line and works on cross-platform, available for Linux, macOS, and Windows. Crowdin CLI is a developer tool that helps in creating and managing translation files using the CLI. Crowdin CLI is open-source and available for everyone to use.

While the Crowdin CLI can be used with various CI/CD tools, the Crowdin GitHub Action is a specialized tool that uses Crowdin CLI to automate localization workflows directly within a GitHub Actions environment. This provides a more integrated experience for projects hosted on GitHub, allowing you to automatically synchronize localization files and even create pull requests with new translations, ensuring all changes are reviewed before being merged.

How to install and use Crowdin CLI in your project?

You can also follow the official Crowdin CLI documentation. This is the best for everything related to Crowdin CLI. Now, I’ll also walk you through how you can use it:

Here is how the whole workflow works:

Your Project ➜ Crowdin CLI ➜ Upload Source File ➜ Get the Translation Done ➜ Download Translated Files ➜ Deploy

Step 1: Install Crowdin CLI on your system. For JS, it’s recommended to install with npm. You have other options as well, like brew, choco, Docker, etc.

npm install -g @crowdin/cli

Step 2: Create a configuration file in the root of your project:

crowdin init

Here is how it will look:

"project_id": "projectId"
"api_token": "personal-access-token"

"preserve_hierarchy": true

"files":
  [
    {
      "source": "/locales/en/**/*.json",
      "translation": "/locales/%two_letters_code%/%original_file_name%"
    }
  ]

Step 3: Get Your Credentials

• Project ID: Found in your project settings
• Personal Access Token:
  • Anyone can generate a token. Manager-level access is required for managing projects.
  • Go to Account Settings
  • API
  • Personal Access Token

Step 4: Verify that your configuration is correct.

crowdin status

Step 5: Upload the source file (eg, English language files)

crowdin upload sources

• It used file matches /locales/en/**/*.json, then upload to your Crowdin Project, only once you need to make sure that preserve_hierarchy is true.

Step 6: Get the translation done

Once you have uploaded the file, translation will be done from the Crowdin end.

Step 7 Download the translated files

crowdin download translations

This will create language-relevant files like:

• locales/es/folder1/strings.json (Spanish)
• locales/de/folder1/strings.json (German)
• locales/fr/folder1/strings.json (French)

Simplest workflow with Crowdin CLI:

# 1. Upload new or update files that need to be translated
crowdin upload sources
# 2. Check how much translation is done
crowdin status
# 3. Download the latest translations
crowdin download translations

Crowdin and Trustpilot: Localization Case Study

Let me introduce a big brand that actually uses Crowdin as its localization platform, Trustpilot. A well-known review platform worldwide.

Company: Trustpilot

Industry: Online Customer Review Platform

Markets Served: Trustpilot is the major player in the review system, which serves in 7+ main languages. One thing is really important to know here because it’s a reviewing platform, so it is a customer-facing platform. That means it gets more and more reviews from customers, which means a broader audience is posting text on the platform.

Initial Situation: After a couple of Trustpilot launches, it grows so quickly. The demand for credible proof of trust becomes essential for almost every small to big brand. This demand starts coming from every region. One thing required to make reviews feel local. Traditional workflows require separate localization of UX writing, which always gives issues in the long term.

The Localization & UX Challenge

Initially, Trustpilot’s localization flow was a mix of manual and little automated — separated translators for different languages, processes are aligned, and content is growing enormously, so backlogs in the content part.

• Manual file handling
• Slow-moving forward to regional markets

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Sometimes, our team is referred to as the ‘translation team’ – but I see localization as so much more than translation. We need to bring attention to how good user experience may mean different things in different markets – merely translating content can never be enough.

Why Crowdin: The Major Turning Point

After getting enormous demand, quality content becomes a priority, and then Crowdin comes in with a solution.

• Automate integrations - Crowdin localization support almost in every possible manner, from localization of the content to website content, marketing copy, Zendesk kind of support, and more.
• Enable scale and quality - The problem of handling a high volume of content is also handled by Crowdin very easily. It’s an AI-based Localization platform for JavaScript and not even JavaScript, but for almost all languages, making it a versatile, quality-focused, and ready-to-use platform.

Quantitative Results

• Total Language in which Trustpilot Localized: 7
• Crowdin Integrations: Crowdin offers integration with GitHub, and it also helps in translating marketing copies.
• AI/MT Utilization: It’s a combo of artificial intelligence, along with humans in the loop for quality assurance.

Stat Highlights

Conclusion: Best Time to Use Localization for Your JS Apps

JavaScript localization is an avoidable problem for businesses that are targeting globally or are planning to target global markets. This can become your investment for the future that will help you in gaining users’ trust, a first-mover advantage, and open new opportunities to scale. Adopting modern technology-based platforms like Crowdin can turn your codebase into multilingual applications in no time. Crowdin ensures quality by looping humans in the system and quantity by using AI - a real localization engine that will boost your business revenue.

Useful links

• GitHub Repo
• Vercel Link

FAQ

What is localization in JS?

In simple words, localization is a way to map the content languages according to the region from which visitors see the application, software, website, etc. Localization is all about adopting or, in other words, converting the whole system to a regional system, like we’ll have to convert:

• Language,
• Culture-based formatting,
• Date/time formatting,
• Measurements and other conventions for each user. To make everything feel native.

How do I localize a JavaScript app?

There are two steps involved in localizing your JavaScript application:

1. You have to internationalize it first using i18n, which tells whether your application infrastructure is ready for localization.
2. Then you have to use another standard that is called localization l10n.

With the combination of these two, here are a couple of more things we need.

1. Translation file
2. JavaScript Libraries like i18next, LinguiJS, or platforms like Crowdin.

Then, after, we have to go around the locales in which we want it to work.

What is the difference between language and locale?

Language conversion can only change the vocabulary or grammar, so you can convert one word to another. But in locale, this not only uses languages to convert, but we also have to change the region-specific formats. So a date might be written differently in French, and it might be written differently in Japanese.

Why not just use Google Translate?

The first thing that I have seen with Google Translate is that it doesn’t work properly on intent-based content. If you have written something, then in Google Translate, it might convert it to something else, and the meaning will also be different. Not only that, there are some nuances, accuracy problems, and context issues. This is the only problem that can be solved with the human-in-loop, and who knows about both languages.

Are there any legal/regulatory reasons to localize?

The short answer is yes, many countries want the software to be worked into their language, let’s say Germany, China, Indonesia, Brazil, India, and others.