Applying OpenType features in webfonts is a two step process. Typotheque webfonts are always generated for a specific webfonts, based on the requested language coverage and by default the OpenType features are removed. First, we need to make sure that the characters needed for the OpenType substitution are available.
If you use fonts in Adobe applications (InDesign, PhotoShop, Illustrator), and the fonts are missing or appear corrupted, search your computer for all copies of the file AdobeFnt.lst (for example, Adobefnt01.lst ... Adobefnt12.lst) and delete them. The easiest method is to search your hard disk for all .lst files.
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).
Just go to Glyphs, on the font presentation page.