And we haven't even talked about languages with dual as third grammatical number

That is kinda what I'm talking about. Like I wouldn't be able to explain how pluralization works other than instinctively knowing what's the right plural for each case by case word. English slapping an "s" at the end is a breeze.

Not by name, that's for sure ^^

corrupt .. I kmow I am late to the party .. but how does "Die Berge" fit to northern Germany if there are no mountains? ^^

Ah, "only" 5. Still. To a German brain, that's one too many ^^

Isn't Romanian also one of the ones with like seven cases? Slavic languages are brutal to learn.

Except you talk about countries like India, Pakistan, and Bangladesh, where it literally was the language of a brutal colonizing force for over 200 years.