bad imitator

Hi,
<He has an agile tongue.> (= He can pronounce foreign words correctly)

I’d like to to learn an expression with the opposite meaning, for somebody who finds it difficult to imitate foreign speech. Is there any at all?
Thank you.

Thank you, mjd.
Well there's always a way, but I guess there isn't anything common.
What about "He has a clumsy/slow tongue"?