彼は外国語の上達が早い。の英語

He is quick at learning a foreign language.

He is quick at picking up languages.

I'm amazed at his rapid progress in English.

He improved at English suddenly.

He is getting better at English than before.

I'm amazed at his rapid progress in English.

His English is improving.＝He's improving in English.

He has make remarkable progress in English.

His English will improve in the course of time.

He's behind the other students in English.

I am sure that he will get even better at English than he is now.

He is advanced in his English―forward in his English―well up in his English.

he taught foreign languages

He's anxious to improve himself in [at] English.

He is especially proficient in English.

He speaks English well.

He acquired French quickly.

He is a good speaker of English.

He is good speaker of English.

He has increased his proficiency in English greatly.

He is getting on very well with his English.

He is good at (foreign) languages.

He has a good command of foreign languages.

He is quite at home in English.

He is such a good English speaker.

I wonder if he became better at speaking Italian.

He speaks English well.

He mastered English easily.

His English abilities are really excellent.

He is ahead of his class―in advance of his class―in English.