Hey this is pretty timely! Just yesterday (a few hours after this post) I released a new version to hopefully fix this stuff. Please let me know if everything is working for you or if you ever see this error again!

Basically each instance has a list of all languages it knows about (“all languages”), instance admins can chose which languages people are allowed to use (“discussion languages”), on top of that community moderators can further restrict which languages people can use in their community, and further still you can select in Lemmy’s settings which languages you chat in. All of these can impact which languages you’re allowed to select in the language dropdown on posts/comments.

Alexandrite wasn’t doing anything with the languages before really, it was just presenting you the full list of languages the server knows (“all languages”) and letting you freely pick (defaulting to “English”), even if they weren’t valid. Now it should be respecting all the rest of the restrictions/settings I mentioned above.

@freamon@endlesstalk.org is exactly right, looking at your posts you were posting in !news@lemmy.world, with the new Alexandrite update I’m only seeing an “Undetermined” as an option. If you were trying to post in English before (which is generally the default Alexandrite attempts to use) that would probably result in this error.