This translation project is there for the free android APP "Activity Diary" with that you can track your activities. Each contribution is - by the act of transmitting to this project - released by the author under the terms of the "GNU General Public License v3, or later".
Before contribution ensure you know the project, have used the app and are familiar to the README.md
in the project, espacially the section about contribution, as this also applies here to the translations.
Also please do not ask to become a proof-reader, if you actively participate you will become a proof reader. It is best practice to just start translating and voting for the good translations, or suggesting improvements. Also check the comments for other languages, to see what is important. For doing a good translation I think you should use the app for some time to understand the context. A good translation is not a word-by-word accurate text, but a translation that uses the same terms as in other programs or e. g. on wikipedia for some things, like the mentioning of the GPL, whether those terms are translated or not. Sometimes it might also be necessary to pick a "bad translation" to make it fit into the UI, in those cases please get in contact we the author of the app.
After you contributed a substantial part to a language please get in contact we the author and share you name and an URL (if you want), that you can be mentioned as contributor in the about view.