I can see why someone would want that, not only due to the potential differences in levels like you mentioned, but also because the type of content people consume may differ from language to language: imagine following someone because you share their love of reading German philosophy only to discover their Japanese feed is nothing but magical boy BL manga… (Not that you can’t love both!)
On the other hand, I want to see what everyone’s reading in all their languages.
I think this would be a worthwhile addition to filter out content that isn’t suitable for your current level, especially in the global feed.