While it may not at the frontend (in that you would have to go through "manually") if you had the German in one style and the Polish in another style, that would make identification after the easy. You could make each language style have a shortcut (say Ctrl-g and Ctrl-p) which would make assigning the style fairly easy. You can move through a document pretty fast that way.

And if certain characters CAN be used in a paragraph to identify a language then using that to assign a style could be automated. The point being is that once separated by style (and of course the different styles could look the same in terms of FORMAT) performing actions (like hiding them) on the style/language is straightforward.

The above may not help. Just a thought.