p.s. For anyone wondering what the post language setting is even for, it allows people to easily filter out posts in languages they don't speak, and also provides a "translate" button below your post if people don't speak your language.
However, this system relies on people using the correct language settings for their posts, so that the system knows which language each post uses.
You can find out more about language settings on Mastodon in the guide at https://fedi.tips/setting-your-language-preferences-on-mastodon-and-filtering-out-posts-in-other-languages

Setting your language preferences on Mastodon, filtering out posts in other languages, filtering search results by language | Fedi.Tips – An Unofficial Guide to Mastodon and the Fediverse
An unofficial guide to using Mastodon and the Fediverse
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