I don't know if/ how hard this is required. I guess, other languages would be more required
As far as I can see, there is a lot of german people working together with the Arduino team already^^
I'm curious, why do you say that? Is English language fluency so common for native German speakers that the lack of translated documentation is no barrier to their success with Arduino?
None of them have done any work to start the German translation. You can see the reference-de repository is completely untranslated:https://github.com/arduino/reference-deIt seems the way the translation projects have been working is an Arduino community member that shows initiative is given administrative privileges in the repository. I think the translation is expected to be done as a community project rather than by Arduino employees. The Arduino employees are more involved with the infrastructure side of the project.
Certainly I wouldn't expect much success for most young people here in the US trying to learn C++ and electronics when the majority of the available information was in a foreign language. I think most would just give up and go back to wasting their time on Snapchat.
I see the German translation of the Arduino IDE is 99.7% finished so there definitely have been some people involved in German translations for the Arduino project. I haven't noticed Arduino doing a very good job at advertising the documentation translation project so maybe people are just not aware of it. I don't follow the non-English forum sections so maybe there have been calls for volunteers there.
In addition to the initial work of translating the reference pages, there is the ongoing need to mirror new improvements made to the reference-en repository. The Arduino team set up a nice system where an issue is opened in each of the translation repositories for every pull request merged in the reference-en repository.
Of course there are no obligations. The great thing about open source projects is that even small contributions from many people can add up to something really amazing!