Additional features, settings, or issues not covered by specific Microsoft Teams categories
Same here. I'm in Germany, multilingual spell check works everywhere except for MS Teams (New Teams, version 25094.310.3616.953, enforced by company).
I seem to be able to add and move a second language in the MS Teams general settings, but as soon as I go back to settings it just disappears again. Pretty annoying that a bug from late 2023 just reappears like that. Especially after it worked for me as of a few days ago.