how common is the sentence?

Hello!

Is thie sentence below common in English?

What he advised them was a suggestion to improve their communication skill English.

Thank you.

'Advised' makes 'suggestion' redundant.

I would write, "what he advised was for them to improve their communication skills in English".

Some of that seems redundant, so I'd phrase it as:

He advised them to improve their communication skills in English.

I agree with nic if it isn't necessary to refer to a previous statement with "what he advised" as the subject.

If modified to "What he advised them was to improve their communication skills in English", then it is grammatical and makes sense, at least, but even still, most native English-speakers would probably not put things that way in most cases.