Typotheque fonts are Unicode compliant, so you need to enter your text correctly encoded. An easy way to find out if you have correctly encoded text is to copy-paste a sample of the text into Internet browser, for example into Google search.
Some old text documents working with Arabic or Indic languages use 8-bit encoding, which required to use proprietary fonts. Such fonts can only use 256 glyphs, which is not sufficient for correct rendering of Devanagari (or other 10 Indic writing scripts).
LetterMeter, a Unicode based text analysis tool, helps compare multilingual texts and measure the frequency of particular glyphs. It has been moved to a different website: http://www.type-applications.com.
Typotheque offers Multilingual Unicode Compliant Fonts in WGL4, and larger character sset supporting over 80 languages in standard Latin, Central European, Baltic, Turkish, Greek, Cyrillic, and Arabic encodings.