Chinese native speakers' English

[Englishlanguage]

Correction
I'd go for the first one. If he used a translator, there would be no need for the company he works for to have him. The translator could make phone calls to China, and the company would pay one wage/salary instead of two. (Note, but is the translator able to do the man's job?) Anyway, how he communicates with his Italian colleagues remains a mystery to me.

Does that help?

Thank you.
Is there any better expression for this sentence
how he communicates with his Italian colleagues remains a mystery to me,
Could I say how he communicates with his Italian colleagues remains unsolved or remains unknown? Do I convey the same meaning?

[Tdol]

'Remains a mystery' sound much more natural than those two to me.

[Englishlanguage]

Thank you Tdol.
The other ones don't sound good to me too. I just gave a try!