Using kate, I struggled with files with "unknown" or "broken" encoding many times. What I think is needed is a way to enforce a certain encoding (which there is), *and* have kate show the characters that are "wrong" (at least say in which line they are). Optionally, it would be great to have the choice to simply replace them by a given character, or just drop them. I just had a file that had a NUL character in it. "iconv" did not remove it, and kate pestered about illegal characters but did not say where they were. Reproducible: Always I classified this as "wishlist".
*** This bug has been marked as a duplicate of bug 366727 ***