"Are there a large number of Hungarian speakers?"
Even that sounds awkward to my British ears - I'd personally say something like "do a lot of people speak Hungarian?". If my question was about how many people spoke it outside of Hungary, I'd say "is Hungarian a widely-spoken language?".
"Suuri" could also be translated as "great", meaning something big in stature. Which could be what they tried to convey here, but using the word "great" is not accepted.
In Finnish this sentence is ambiguous in meaning, although I suppose grammatically not as bad as the English "large language".
The sentence does makes sense in other languages than English. You could (and should) express it other ways in English, but then the "translation" wouldn't make sense. At least not from a learner's perspective, with only basic grasp of the Finnish grammar and vocabulary so far.
I really feel somewhat stupid, but I think I still haven't understood what the exact meaning of "suuri kieli" is. Does it mean "widely-spoken" or "which possesses a large number of words"? Or anything else maybe? And what about "pieni kieli"? Could a native speaker explain this, please? Thank you so much!