Product file encoding?

[NLP-er]

Hi.

What should be product file encoding to include there diacritical signs?

I'm trying to set some Polish letters there (like ąęść...) and I set for product file
<?xml version="1.0" encoding="ISO-8859-2"?>

But polish letters are changed to ? signs. Same when I did it in UTF-8.
I'm programing in Eclipse for PHP which automatically writes file in appropriate encoding recognizing by mentioned line.

BTW. when I correct those ? signs in Admin CP then it is OK, but creating plugin from product file those signs are changes.

So how to write product file with diacritical letters?