Because in high school, we only covered grammar and reading comprehension.
I'm not good at speaking English because in high school we only covered grammar and reading comprehension.
ご質問ありがとうございます。
「高校では、文法と読解しかやらなかったから」は英語で「Because in high school, we only covered grammar and reading comprehension.」と言います。
もし、もっとはっきり言えるように「なぜ英語喋れない」という質問に対して、「I'm not good at speaking English because in high school we only covered grammar and reading comprehension.」という風に説明できます。
ご参考になれば幸いです。
It's because in high school we only did grammar and reading comprehension...
"高校では、文法と読解しかやらなかったから..."
- It's because in high school we only did grammar and reading comprehension...
- That's because we only did grammar and comprehension in high school...
日本の高校での英語の授業では、文法と読解しかやらなかったから...（喋れない）
- In Japanese high schools, because we only do grammar and reading comprehension...we can't speak English.
アメリカ合衆国 
