You can easily add more languages by adding/overwriting string resources.
HINT: This is not only true for strings. You can exchange all localized resources (e.g. add icons for different languages).
For more information take a look at the Developer Guides.
Using the localization editor
Copy and paste the downloaded files (just the files, not the folder) into the
res folder of your own app. Afterwards, open your project in Android Studio.
res/values/string.xml (if the file doesn’t exist, you will have to create it) and click
Edit translations for all locales in the translations editor. ->
Now you’re able to edit all texts and translate them into other languages.