There are two types of content that need to be translated: videos and strings (text). For videos, you can translate subtitles, dub or recreate; for strings, you can translate text from exercises, articles, descriptions and the platform (website & mobile strings).
Keep in mind, however, that the specific material that you translate depends on which language team you translate for (some teams have been active longer than others, for example, and are focusing on different items than newer teams). Volunteers will have information about what to translate on our Translation Portal. If you want more information about which topics you will be translating first (typically math content) and whether you should be translating videos, articles, or platform language, please check in with your language advocate.