- more varied vocabulary... - more varied grammatical structures...

This is very literal. Imagine that you know 500 vocab words in a language. That is your "range of language." (Range meaning your current available amount) Now imagine you learn 300 more words. You now know 800. Your range has become "more wide." You now have a "WIDER range of language."

If you describe something as wide-ranging, you mean it deals with or affects a great variety of different things. I hope it helps 😊👍