"I don't know why the English language has so many different subject pronouns."
"I don't know why the English language has so many different subject pronouns."
"I don't know why ~" 「なぜ〜のか分からない」
"the English language" 「英語という言語が」
"has so many different" 「の数にそんなにこだわる」
"subject pronouns" (I,you, me,etc.)「主語」
[主語](https://eikaiwa.dmm.com/uknow/questions/55875/)についてもっと詳しく知りたい方はクリックしてください。