I've had this happen randomly in both Liftoff and on the web. The fix I've seen is to change the language from undetermined to whatever you use, English for me.
I have this on the post you linked too, but also on some, but not all, comments from other servers. The workaround described here doesn't seem to work for everything for me.
This is happening to me too. When I click on the select language drop down list on the mobile Web site only undetermined is available and I am not sure it is actually being selected when I click it. I'll see if this posts.
Ok that worked However I have tried to post a comment under the following post in the Coffee community, which I am a member of, following the same procedure that worked for the above comment: type something; click select language; click the main body of "undetermined"; select language box gets an orange outline; click post.