@es0mhi not quite sure what you're describing, are you saying that like an english sentence will randomly have words from another language in them? I mean, we all have to look up words we don't understand in our own languages, it's not that different if you're just typing "define: ___"in google.
That said, if you're intentionally posting in a specific language, the post can be marked as that language (at least if you're using the website, client support varies) and mastodon has the ability to filter by language.