Bangla Unicode fonts are used in this site. If you can’t see Bangla fonts, most probably you need Bangla Unicode font and you may need some additional tool (or tools). These are freely available on the internet.
I recommend SolaimanLipi font. Installation of only this font may solve the problem.
Visit www.omicronlab.com and Install Unicode Complex Language Script and Install Bangla Font.
Visit www.ekushey.org and install required font and tools for free.