Hey guys, i remember years ago when i was playing homam 4 with czech localization. Why isn´t czech language included in gog version? Is there a way how to put it there?

Because rights for that need to be secured.

sorry for necro, but it was CD PROJEKT (czech) who did the translation/distribution of the game here, so not sure why isnt czech language ( it was even czech voiceover) included..

GOG isn't a direct heir of CD Projekt's distribution activity. We also have to remember that acquiring the rights to localized versions of games isn't that simple. Some third party entities can be involved, which for some reasons might not be interested in providing the permission to use the translation.