If you are see boxed font in your opera min browser while browse some website language like Bangla, Hindi Other Complex scripts Fonts.So you can see Bangla font in your Opera Mini Browser.
Type opera:config or config:
in you address bar where you type web site address and open it. find out Use bitmap fonts for complex scripts and Enable it from disable.Then Save it.
Now Browse any site which has Bitmap Fonts like Bangla font , Hindi font and other Fonts.