The Steam version of the game includes italian language, but the GOG one is only english. GOG please update it :(

Just a random guess that whatever agreement GGO made with the developer does not include translations, either because 1) GOG didn't feel like needing it, 2) GOG couldn't predict future translations and so didn't think of including them in the agreement, 3) someone other than the developer owns the rights to the translation (most likely the translator themselves) and they just sell the permission to use it, and GOG would have to buy the rights separately.