QWEEDDYZ: i dont remember, either it is come with language switcher tool (gog use that for some games to change ini/registry/swap folders), or as above post suggestion - manually edit hospital cfg file into
ENG FRE DEU SPA ITA or SWE
There are some alternative methods to change the game's language without editing files, but it seemed better just to offer the simplest available solution with the fewest steps that was guaranteed to work.
It's possible to, in GOG Galaxy, select the desired language from within the settings menu for Theme Hospital, but this requires Galaxy to be installed; it's also possible to select the game language when installing the game from the offline installer, but this had no effect for me and installed the game in English anyway - possibly because of some residual file directing the game to be in English.
Either way, I didn't find a language switcher tool (Language_setup.exe.) within the directory.
https://support.gog.com/hc/en-us/articles/4412958845329-How-do-I-change-the-game-language?product=gog