Hello,

I installed the game via GOG Galaxy and chose the German version, but the game starts up in English. When I check the settings, I can only see English, French & Italian as options. Is there a way to change to German?

P.S. My Windows installation is English, could that cause the problem?

Try to verify game files.
I guess it indeed take default lang from OS user locale currently set, but thee should be swither to all listed languages.

Did 1.0.5 version showed in Galaxy client? Are you sure it latest? Verify not update it, since Galaxy is allow to stay on differ version builds, it verify as current one.
Try to remove game folder from here (put it in address bar)
%USERPROFILE%\AppData\LocalLow\Toukana Interactive\
if there is saves you want to backup - keep them. If there is no saves or you not really needed them - better start new game - erase entire fodler.

Game is multi- and it can be switched from ingame menu. So better set it English in galaxy client (or offline build). Reinstall maybe, as eng version (but always do validate files after any downaloding, reinstalling not solve anything without it).
├── StreamingAssets (20 Entries)
│ │ ├── localizedText_Arabic.json
│ │ ├── localizedText_BrazilianPortuguese.json
│ │ ├── localizedText_ChineseSimplified.json
│ │ ├── localizedText_ChineseTraditional.json
│ │ ├── localizedText_Dutch.json
│ │ ├── localizedText_English.json
│ │ ├── localizedText_French.json
│ │ ├── localizedText_German.json
│ │ ├── localizedText_Hungarian.json
│ │ ├── localizedText_Italian.json
│ │ ├── localizedText_Japanese.json
│ │ ├── localizedText_Norwegian.json
│ │ ├── localizedText_Polish.json
│ │ ├── localizedText_Portuguese.json
│ │ ├── localizedText_Russian.json
│ │ ├── localizedText_Spanish.json
│ │ ├── localizedText_SpanishLatinoamerica.json
│ │ ├── localizedText_Swedish.json
│ │ ├── localizedText_Turkish.json
│ │ └── localizedText_Ukrainian.json

Thank you, now I managed to swtich in game. I don't know why the language list didn't scroll down yesterday, today it did and I was able to reach German.