He is said to be expert in English speech.

据说，他擅长用英语作演说。

Be expert in...

在…方面是专家。

For example, individuals need to be expert in their specialty areas to move up. That tends to preclude branching off into other areas of the community.

例如，在某专业领域成为专家的人也需要不断改进，需要排除异心与智囊团的其他部门协作。

He claims to be an expert in astronomy.

他声称自己是天文学专家。

I don't profess to be an expert in this subject.

我不敢自诩为这方面的专家。