language selector can change into regional variants, causing overflow

[trwnh]

Steps to reproduce the problem

start typing a long status in (us) english?

Expected behaviour

language stays constant and two-letter code format

Actual behaviour

language changes from "en" to "en-us" causing an overflow

Specifications

[trwnh]

seems to no longer be occurring

[trwnh]

reproducible: reply to this post https://libranet.de/display/0b6b25a8-1263-7070-b1d5-f51340860275

[mcclure]

Still experiencing this, see example in #23990

The "reply to this post" @trwnh sees above is probably due to the fact that replying to a post will cause its language to be copied into your own post

A second symptom of this same bug: when a viewed post has a region/dialect selector, Mastodon will offer to "translate" even if it is the same underlying language. It does not make sense to offer to translate from "en-US" to "en", and DeepL does nothing but present a 503 error if you ask it to try. My expected behavior is that Mastodon would have some logic/data table for which dialects do and do not require translation (for example, en, es and pt dialects are all mutually intelligible; zh-Hans and zh-Hant probably need a translation offer although it probably technically does not require a machine learning service), omit the "translate" link if it is unnecessary, and strip out the dialect code if including it would confuse deepL (if en-US causes an error, then probably so will pt-PT).