日本語と英語は、文法だけなくて、考え方随分違うらしい。
It is saying that: evidently, the way of thinking in English and Japanese is extremely different.
What does the 文法だけなくて? (Grammar only ...?) I always get confused when なくて appears in a sentence. It is as if i am bracing for some contradiction or negative.
Is their a general phrase pattern for 「~なくて」？
The sentence should be:
日本語と英語は、文法だけでなくて、考え方も随分違うらしい。
「XXだけでなくてYYも」（or 「XXだけでなくYYも」「XXだけではなくYYも」「XXだけではなくてYYも」etc.) means "Not only XX but also YY".
So it literally means:
"As for Japanese and English, it seems / they say that not only their grammars but also their ways of thinking are quite different."
→ "It seems / they say that Japanese and English are quite different not only in grammar but also in way of thinking."
Yes, it's say that English and Japanese are, not limited to grammatical aspects, very different languages.
