[nekrosoft13]

I tried every possible setting in Aeon, just can't get Polish characters to show up.

these letters show up: ó, ł,
these don't: ą, ę, ć, ś, Ż,
take a look below, arrows point to missing letters.

[Halibutt]

You'd either have to switch to Polish translation and Polish font, or simply grab a CE-compatible/Unicode font, save it under the appropriate name (check \XBMC\skin\Aeon Stark\fonts for fonts used and \XBMC\skin\Aeon Stark\720p\Font.xml for more detail). The latter file explains precisely which font is used where.

The easy way is to download my translation, rename all fonts ("AkzidenzCond CE.ttf" to "AkzidenzCond.ttf", "dincaps CE.ttf" to "dincaps.ttf" and so on) and copy them over the original fonts. This should work, I guess.
Cheers