First: You can use Zenger's language changer.
Copy to game directory and execute.
Download:
http://ul.to/9bqwlogw Or you go this way-->
* Text+Speech: English, French, German
* Text only: Brasilian, Dutch, Italian, Spanish
* Go to <game>\data\voices\<the-language-you-want>, select all the files and copy them to the root installation folder (<game>), it will replace the text.pak and the fix.pak files(that's all for Brasilian, Dutch, Italian, and Spanish), for French and German, delete the voices+.pak files. and rename the new ones to add + to the file name (for voicesge.pak you have to add n+), so you will have the same filename as before.
* If you want one language for voices and another for subtitles, first copy everything as above for the "voice" language, then copy just text.pak and fix.pak for the "text" language.
(thanks Nodens and cebewee)
Beschreibung ist aus dem GOG Unterforum und funtioniert perfekt ;)