In game The I of the Dragon is on Steam writed game have 4 dubbings included CZ but on GOG is only EN and DE, it is mistake or really GOG version haven´t CZ localization?

I would like to buy such an old game on GOG because here I have more certainty that the game won't stop working as it sometimes happens on Steam because old DRM and moreover here it has Windows 7 fix but honestly for CZ dubbing I would go to Steam because nowadays there are almost no such games anymore.

No, it does not have it. As for why, I have no idea.

The rights to offer/sell a specific localised version of a game on a specific platform sometimes have to be negotiated separately (that's the assumption at least) and Topware Interactive seems to have been unable to secure the Czech as well as the Hungarian localised versions for the DRM-free GoG release.
Who knows, the exclusion could also have happened deliberately to make the DRMed version more attractive or over unreasonable terms in the contract GoG wasn't willing to accept.

Maybe there's a Czech language patch floating around on the net you could apply to the GoG version?
Or, in case there isn't one, maybe someone could put together that Czech language patch and then make it available through the I of the Dragon subforum here?

Well, I do have the game on a disc with the czech assets. Wonder if simply copying the files into the GOG version would work?

Gonna try.

EDIT:
Well I can get the Czech voices and intro in, but text strings don't show up properly. But you could play with Czech voices and english text.

The text problem is probably related to a missing font or formatting for the czech symbols. All places where text should be are either blank or filled with black boxes.