[Eiyu*Senki Gold] How to change a Font?

[sim22x]

I want to translate Eiyu Senki GOLD - The New Conquest to another language. But I don't know how to change the game's font.

I unzipped the System.dat file. It contains the game fonts in a format I don't recognise .rsf.

There is a file called Font.txt. One of the fonts is listed as System MS Gothic.  But I can't change it to another font, the game crashes. 
I can install another font called MS Gothic on the system, but the game won't use it. Maybe the font is specified in the .exe file?

 In short, I'm at a loss. 

Game files: https://pixeldrain.com/u/fptLYdSQ