Hi! As far as I know a warning about Undetermined languages should show up in a box in the Settings page, but instead the text “undetermined_language_warning” shows up. I think that’s a bug.
Before lemmy.ml was down I remember the message correctly showing on my account on that instance.
I get that same error message as well, and I get something similar when posting on other instances where “undetermined” is an unsupported language. (I initially took this error as a warning about foul language which confused me for a bit.)