Yes and no

We did it with a german version, long ago... so I don't know the details anymore, just the general idea.
First of all, the german CD key did not work with the original D2. We then replaced files, one by one, skipping the ones that made bnet complain about the key not matching the program version.
In the end, we got a version that is "mostly" english. NPC talking is still german (just the audio, not the scrolling text) for the classic samples (I think... the samples that got added with LoD are english, IIRC --- I try to not get to hear too much of the terrible german dub, so I use the german version for mules/rushing).
I'm running some comparison on the 2 directories now... maybe it turns up something useful..
EDIT: crap.. I wish I could make shares on my XP box (for some reason I never managed to do that...) and import them on my Linux box (that one isn't set up to import shares), so I could cut&paste the results
In any case, it appears that (unless I overlooked something... alway possible):
d2music.mpq
is reasonably different. Maybe try the french version first.
d2char.mpq
d2exp.mpq
d2sfx.mpq
are almost identical. I would probably try to use the english files here to start
patch_d2.mpq
is mostly different
d2speech.mpq
is completely different, so most likely that's the one that will need to remain localized
d2video.mpq
isn't installed in my german version
I ignored readme, logfiles and similar stuff.