>>38 文意は通るんだけど、ちょっと添削。
The second sentence is what you'd call a "sentence fragment". Grammatically it sounds correct, but on its own it's actually incomplete. To make this sentence correct, you should combine it with the previous one. "Absolutely, Japanese is harder to master than English, so I respect you for mastering Japanese and even kanji."
2. America is nation of immigration and so the language become easier. On the other hand, There is little immigrant in Japan and the language get specialized.
Missing particles, count/non-count mistakes and incorrectly conjugated verbs. "America is a nation of immigration and so the language becomes easier. On the other hand, there are few immigrants in Japan so the language is specialized." would be correct.
3. You said Japanese who uses English well is rare, but I can use as like this post with compulsory education.
Incorrectly conjugated verbs. The second half also doesn't make much sense - you should consider re-writing it. "You said Japanese who use English well are rare, but I can speak English at the level of this post with only compulsory education."
間違いを直すんなら自分の文法から始めましょう。(・∀・)