Do you know a tool to decode "UTF-8 twice"

I have a database with broken encoding, containing a lot of "UTF-8 twice"

(that infamous encoding that arises when UTF-8 is interpreted as latin-1 and

converted to UTF-8 again) encoding besides ASCII and UTF-8 proper.

 

Is there a ready made tool that decodes "UTF-8 twice" while keeping UTF-8 proper in place?

 

--Jörg Knappen