My teacher was talking 90%, but it was good to practice my listening skills.
My teacher was talking most of the time, but it was a good listening exercise for me.
ご質問ありがとうございます。
まず、「9割方先生が喋っていた」というのは
My teacher was talking 90%
My teacher was talking most of the time
と表現することができます。
そして「リスニングのよい練習になった（よかった）」
it was good to practice my listening skills.
it was a good listening exercise for me.
ご参考になれば幸いです。
The teacher did about 90% of the talking, but it was good listening practice.
The teacher did about 90% of the talking, but it was good listening practice.
Most of the class was the teacher talking, and it really helped my listening.
「9割方先生が喋っていた」という部分は、英語では **about 90% of the talking** や **most of the class was the teacher talking** と表現するのが自然です。
日本 
アメリカ合衆国 
