This works for me (output attached):
\documentclass[10pt,titlepage]{book}
\usepackage{xltxtra}
\usepackage{polyglossia}
\setmainfont{Charis SIL}
\defaultfontfeatures{Mapping=tex-text}
\newfontfamily\textsanskrit[Script=Devanagari,Mapping=RomDev]{Sahadeva}
\begin{document}
Hello world!
\textsanskrit{astyuttarasyāṃ diśi devatātmā\par himālayo nāma nagādhirājaḥ}
\end{document}
But I think there's another point. You've gone through some trouble to
convert Velthuis to UTF8. But if, in the \newfontfamily statement you said
"Mapping=velthuis-sanskrit" then the Velthuis encoding itself can give
perfectly good Nagari output.
E.g.,
\newfontfamily\textsanskrit[Script=Devanagari,Mapping=velthuis-sanskrit]{Sahadeva}
\begin{document}
Hello world!
\textsanskrit{astyuttarasyaa.m di"si devataatmaa\par himaalayo naama
nagaadhiraaja.h}
\end{document}
Best,
Dominik
kk.pdf
Description: Adobe PDF document
-------------------------------------------------- Subscriptions, Archive, and List information, etc.: http://tug.org/mailman/listinfo/xetex
