[KaktoR]

I have uploaded a attachment with your original script inclusive the code you need and each system.cfg file. Use this as reference.

I've tested this with 3 languages (german, english and italian) and it works.
Each xx_system.cfg has its own language at last line (en_system.cfg -> g_language="english", de_system.cfg -> g_language="german", and so on...).

Download attachment, open installerscript.iss and go to line 130 and take a look on this.