We should have a good command of large vocabulary.

我们应该掌握大量词汇。

It should be emphasized that applicants for this position should have a good command of English.

需要强调的是，此岗位的申请者应精通英语。

Have a good command of English.

英语掌握熟练。

I have a good command of English.

我的英语掌握得很好。

You do have a good command of English.

你的英语真的掌握地很好。