This is not about playing the German CD version. I am trying to copy the CD music files (within the German CD version) into the English version of the game.
Sure, however the cause of the issue might be the same.
I am guessing due to some file changes, it does not work and the game doesn't launch when I follow the steps provided in the PC Gaming Wiki link
I can't install the game and check it myself right now.
1. Which CD image do you mount?
Quote from the post, I've linked: There are 2 CD images, "gamea" and "gameb", both are so called mixed mode CDs, i.e. they contain a data track as well as CD audio. The images are CUE/BIN images, actually "gamea.inst" is the cue sheet (usually named "gamea.cue"), while "gamea.gog" is the bin file (usually "gamea.bin"). The audio files are stored under the MUSIC subfolder as .ogg files, as indexed in the CUE sheet ("gamea.inst").
PC Gaming Wiki instructions: Copy the German MUSIC, game.gog, game.inst, INTRO.EXE, SCHICKM.EXE and SOUND.CFG to the English installation folder, replacing existing files when prompted.
... Add this line: imgmount D "..\Realms of Arkania 1\game.inst" -t iso
2. Have you tried to use absolute paths instead of relative?
3. Is there any console output / error message when you launch the game?
4. Does German version work fine? Compare it's DOSBox configuration with English version.
5. Do you use DOSBox included with the game? Try to install the latest version from the official website.