About the missing files:
If you add a space after line 12 SET MOD=.exe echo, the batch should have displayed things correctly.
By space you mean additional line (one more "enter"), right? If so - the problem didn't disappear...
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About the text:
If someone copies and then translates the text from the BiG World Installpack\English/German/Spanish/Russian and sends them to Leonardo, it will be placed in you BiG World Installpack\[your language folder].
So talks about English since it's lacking a Polish translation.
If I understand it correctly, you refer to the installation notifications like press (E)nglish to choose English, or ... (S)tandard for standard version, am I right? Just the "user interface", nothing more. Hm... maybe I will take another look into this and translate it.
The logic about selecting languages is taken from the tra.txt. You can see that the file from the English and Polish folder differ. BGT has BGT=0 N or BGT=7 N. So it installs 0 in native language if you select English or 7 (native) if you select Polish.
Is there any way to "force" the Big World Install.bat to chose only Polish translations? I can't get through it - it says "Language: english only" - it's quite disappointing
Many thanks for all information!