The LangCZE.owp (Which contains Czech sound files) contains Ape sounds. Both LangCze.owp and Data2.owp (Which contains English sound files) only have American and Russian sounds. I can't remember but i thought that arabians just used the American sounds.

Have you tried Validating the integrity of your game files?

I have validated game and done some more research (switching languages, trying game) and found out, that neither czech or english unit responses work in first 4 arabian missions, than they do (as far as i have played). I changed language around that time, so I thought language was a problem. Interesting thing is that polish campaign playthrough (that I don't understand) also doesn't have unit responses in first 3 missions but have them in 4. and others. Video was uploaded 5.1.2016 https://www.youtube.com/watch?v=1iu6ZcdxJVs&index=4&list=PLa4DBGfZdBdSALoh5Bq-uQfVhMJRpM8NR

The only thing I can think of is if someone left a DisableExclamations open. It tends to persist over missions. I didn't find any though but I've inserted the reverse function in the beginning of the first mission. Maybe it helps. I couldn't reproduce the bug in the first place.

The change haven't helped. Situation is still the same (I checked first 5 mission starts and saves in czech language, even new player profile and first mission start (I am aware that main character never responds)).
And now game updated and actually made all saves incompatible - game informs that mission script won't run and it really doesn't. But that is problem with any updates to Original War I guess. I'm going to find way to roll back and avoid any updates (including mods).