https://lichess.org, the free for all, open source, ad-free chess server :)

PLEASE READ THIS! Faulty translations can be worse than missing translations.
Be careful with special strings of text you may see while translating, such as %s, %1$s, etc. These special strings (variables) need to be copied from the source string to the translated one exactly, or you will break the display of the text.

Example:
⮚ "Your %1$s rating (%2$s) is too high"
... would become something like:
⮚ "Your Blitz rating (2050) is too high"
... on the website and app.

All variables (%1$s, etc) MUST be in the string. They can be in whichever order that makes the most sense in your language, but they must all be there.
This means that even if it's just the number 1, please use the appropriate variable (e.g. %1$s). Do not spell it out as "one" in your language, or it won't work with the software and your translation can't be used.

Notes on the system and translation process:

If a translation is "approved", it just means the translation is "locked", and that only proofreaders will be allowed to change it. Proofreaders for your language can use this option when they are certain this is the best translation for the English text.

Approval is not required for a translation to be put into Lichess. We prefer the voting system to one individual approving translations, so we rarely grant proofreader rights. All translations go on the website anyway, so your translation counts.

Updates happen frequently but it can sometimes take upwards of a week for your updated translations to appear on the main website. The mobile app is updated less frequently. However, you can be assured that your translation work is taken into account with every update so we ask you to be patient in these instances.

If you are translating to a language not currently on the website, please send an email to contact@lichess.org. In your message, mention the language you translated to and your name on Crowdin. We recommend you translate high-priority items first (website, mobile app & emails) to at least 20%. Once done, please send us a message so we can include your language on the site. You can keep working on the translation while it is being added to our website.
We hope all translations will reach 100% completion one day, but we're happy to have them on our site and app before this milestone.

Crowdin automatically puts the Android logo next to file names, but all files here cover both the website and mobile app.