I'd have to check again, but I don't think the "DECORS" folder is needed.
For the BMP files contained in "I2D\bitmaps\", I'm quite sure you don't need them. If one should be required, it'd be shooting.bmp. A least, between the english and french versions, files contained in this folder are the same.
For "I2D\sounds\", you only need these files :
I2D\sounds\FS001.wav
I2D\sounds\FS002.wav
I2D\sounds\FS003.wav
I2D\sounds\FS004.wav
I2D\sounds\FS005.wav
I2D\sounds\FS006.wav
Other are the same between every versions.
In the "IAM" folder (not "IAM\GERMAN\"), I think there is unecessary files. But it doesn't matter.
For the Tracks, the only one you've to change are the following one :
TRACKS\65.ADP
TRACKS\66.ADP
TRACKS\67.ADP
TRACKS\68.ADP
TRACKS\69.ADP
Although I haven't listened the other, I'm quite sure they're the same between every versions.
Your VOICEOFF folder seems correct. Just the 3 "JINGOFF*.ADP" and "ZVOPG001.ADP" that I believe unecessary.
And about the missing voice, it's because you haven't put any *.3DM files contained into the MORPH folder.
I can't be sure at 100%, but here's the file list I believe required :
→
http://pastebin.com/pNbkrPVt And, ultimately, if you'd like to get more information on files required to make a patch for Omikron, and eventually collaborate to build the "best" patch possible, I invite you to consult this thread :
http://www.gog.com/forum/omikron_the_nomad_soul/patch_fr :)
Edit : Yay ! Finally, I can post link.