LSH didn't mod the original Vanilla file. If someone had problems playing the file - maybe they solved the problem by replacing a German cfg file with an English one (it might even be a patch problem - solved by 1.4b).
I don't know the bug and can't help you here, but the LSH team is around...
GWX/A Modder replaced the original Vanilla Yeah/Jawohl soundfile - triggered from sh3.msg or SH3Sound.act or Sound.act or whatever - I don't know.
Obviously they created no new trigger, didn't call the file from an unknown source, but simply replaced the soundfile with another one.
The 'call' at the correct moment is perfectly programmed - somewhere.
To program a new event/trigger/message call, I guess you would have to have the Software Development Kit Ubisoft promised to provide, but refused to hand out.
A Hex Editor and a few intense weeks of try and error might do the job.
But I could be completely wrong here...
EDIT: edit: - no, I changed my mind...
Edit3:
http://www.dependencywalker.com/