oh my god ... I actually found it. I think I searched for something like werecat on IMDB, but somehow I cannot reproduce the result.
however, an english version of the film is on YT:
could not post the link, just type in "Mutator 1989" and you'll find it.
The scene with the human arm is right at the beginning around 6:55. the other one comes later. I'm surprised, the cat monster looks a lot different than what I remember.
Apparently the movie is pretty bad. xD Yet, I still want to watch it entirely to see if I can remember anything else.
Mutator?
That was made in South Africa and was one of the notorious "subsidy films" of the late 1980s. This was Embeth Davidtz's film debut.