'cent' is french for a hundred! In English 100% = one/a hundred percent.

For standard English, it's heading towards confusion. "Cent" is 1/100 of a dollar, so that's the first thing I think of when I read "cent percent". I do realise "cent" is also French for "hundred", but you're more likely to confuse the reader. "A hundred percent" is absolutely clear.

No, it is not.