I usually have kept "undefined" as a language for communities, with the exception of !suomi@sopuli.xyz and !finland@sopuli.xyz.
Meta
Yhteisö instanssia koskeville tiedotuksille, palautteelle, metakeskustelulle ja avulle. Katso myös UKK!
Community for announcements regarding the instance, feedback, meta discussion and help. Check the FAQ also!
Users needing support can also come to our Matrix Space.
Tukea tarvitsevat käyttäjät voivat myös tulla Matrix-tilaamme.
lesson learned for me... the hard way
And to add, those two communities have languages set because I want the first one to be purely in Finnish and the second one purely in English. This mirrors how it is on Reddit.
I ran in to the same problem trying to comment on a thread. How do you get "undefined" in your language list? I only have English
Log on to your instance via browser (not the app) and it should be in your profile settings. 'undefined' is at the top of the list.
Edit: looked closer at your linked post. I see there is only English in your list.
Maybe it's something in the way the instance was configured? That list should be populated with all languages.
Edit 2: spelling