But most posts don’t bother specifying a language and the language is not detected automatically AFAIK. So it’s not too helpful.

Communities can be configured to only allow one language. It’s the case for most of the French speaking communities for instance

There might be an option for you: we can add a #FilQuotidien to the post, and see if that can be federated to Mastodon, and allow you to have a filter based on that.

Sur masto, il faut suivre @forumlibre@jlai.lu: https://piaille.fr/@forumlibre@jlai.lu

Au passage, on avait un post intéressant sur !meta!meta@jlai.lu à ce sujet hier, ça t’intéresse peut-être: https://jlai.lu/post/5116163?scrollToComments=true

No, it only works one way.