With 2.5.x you have to use a different way to install unicode fonts as you're used to. I just tried NiJuLe's method (it's here in the Developer's Corner as well!!!) and it works fine on my 2i:
https://wiki.mobileread.com/wiki/Kind..._2.5.x_Kindles
If there are more questions along the way
this is the NiJuLe's thread.