Starting in Mastodon 4.2.0, you can filter your searches on Mastodon by language.
As no one else has done it, I've written an easy-to-use list of all the language codes used on Mastodon:
https://fedi.tips/language-codes-used-by-mastodon/
Combine these codes with the operator language: to filter your search results.
For example, if you only want Mastodon search results in French you would include language:fr in your search alongside the keywords or hashtags that you're looking for.
Excellent!
One thing I am looking for... It was rumoured that we would be able to choose a setting where those posts we have in our notifications, especially those from people we have followed with the notification bell on, would be sifted out of our home feed.
Can't find it.
You could do that by adding them to a list, and then setting the list to be hidden from your Home feed: