Are there a way to see the encoding of a textfile or a tex-file?
And a way to change it?

I don't think you can 'see' the encoding.

The problem is that different encodings use different graphical glyphs in a different way. In many cases there is no way to figure out how a particular byte (or byte sequence) should look on the screen. You should try different encodings, look at the results, and decide yourself. Of course, sometimes the guess is pretty trivial.

If the tex-file is made in a polite way, it should include a line like
in the preamble. This gives you a hint that the file uses latin-1 (=iso8859-1) encoding.

To re-encode a file -- I guess most of the modern text editors can do it. Perhaps even browsers, I haven't tried. In emacs you have to visit the file (you have to know the right encoding here) and then press <C-x enter F>. Then you are asked for a new encoding.

There are also various command-line utilities (wasn't one called 'recode'?).

Perhaps it helps,
Ott

if you open a document with kate and then go to view you can set the encoding. The next time you save it should save with the new encoding. I'm not sure about how to find out the original encoding

ok.. I found out that it all worked if I use Western encoding instead of unicode.