Exchanging the voice files between BEL and BTCOD is easy:
Just download this tool and extract it. Then drag & drop the files WARGAME.DIR/WAR_MP.DIR (they are inside your BEL/BCD directory) onto ComDirEx.exe.
Next, open the folders DATOS\RECURSOS\SONIDO\WAVE\ESA of both games and exchange the WAV files.
To extract the files from the games Commandos 2 & 3, use the PCK Manager which is part of the Commandos Developing Toolkit.
The voice files are located at DATA\SONIDO\ESA.Go to the full post