Some of the older translations that we have (eg Urdu etc) haven’t been updated for some time, so there might be some strings that are in more recent versions of the app, which will appear as untranslated.
If anyone in the community has the time/inclination and language skills of course(!) it would be great to get these updated.
The specific files for the languages are in the
values-<language code> directories at: https://github.com/DigitalCampus/oppia-mobile-android/tree/master/app/src/main/res
For the translations, you don’t need to be a programmer, just know the language and be able to use a text editor program (like Notepad).