(I'm currently at a crossword puzzle tournament in a foreign language in a foreign country, when I could of course find many such tournaments in my own country... so I guess I've been spending the whole weekend enjoying an experience of appreciating a foreign language in a way that's in some tension with what you describe.)
I didn't understand how to use "whom" in English until I learned (some) German, and I feel that I understand more nuance and subtlety in my own tongue as a result. Same goes for the (sadly nearly dead) subjunctive form.
Language appears to be the tool we use not just to communicate, but to encode our thoughts. It gives us a way to wrangle the abstract from something ethereal and unmanageable into a conceivable thing we can handle. Having many different languages yields many different ways of thinking, not just communicating, and we are impoverished for their death.
This is a fascinating story about the experience of a deaf person who had no language until their 20's. It affected their thinking in an utterly profound fashion - not just their communication.