Thanks for the fast reply

The problem is solved and I feel almost too embarrassed to say what it was

I wanted to replace the XA files from the English version of the with the Japanese XA files and the name of the Japanese one is BOSSINT.XA. There are many others (VOICE1.XA, VOICE2.XA and so on) and they all have the same name in the English version except an underscore with a U (VOICE1_U.XA and so on).
The only exception here is the file BOSSINT.XA which is called BOSINT_U.XA in the English version, they took a S away what I first didn't notice, I just added the underscore and a U

Now the image build just fine and it works

However there is now another problem, even though I could replace all the XA files not all the voices were changed back to the Japanese voice actors. It seems that the XA files contain all the voices that you hear in cut scenes where you can't control the characters but all the "in game voices" (shouts out of pain, when attacking or jumping and so on) are still the English ones.
Are there some standard methods to find out where the data for such sounds might be or how to get them? Beside the XA and STR files there is still a 30 MB big DAT file on the CD and a folder called ARC with many files that end on arc.
Thanks again and greetings

Cossacks