I'm trying to write a document that will contain characters in many different scripts (for which I am using fontspec and rendering with xelatex) and IPA symbols (for which I am using TIPA). Ordinarily, this works fine, however, I want to use slshape for my IPA symbols. If I take the manual's advice and use
\textipa{\slshape f@"nEtIks}
Or
\textipa{\textsl{f@"nEtIks}}
It fails with fontspec loaded. The document renders properly, but the IPA symbols appear upright. If I remove fontspec, then this works correctly, with the IPA symbols slanted. I tried getting fontspec to use tipasl12, but I could not find a way of allowing fontspec to use the font. However I named it, fontspec could not find the font.
This is the LaTeX I have which produces the correct IPA symbols, but they appear upright:
\documentclass[12pt,openany]{book}
\pagestyle{plain}
\usepackage[margin=1.8cm]{geometry}
\geometry{a4paper}
\usepackage[parfill]{parskip}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{fontspec,xltxtra,xunicode}
\newfontfamily{\AR}[Script=Arabic]{Scheherazade}
\usepackage{tipa}
\begin{document}
\textipa{\slshape f@"nEtIks}
\end{document}
The following, however, works perfectly, but - obviously - would not allow me to use Arabic characters:
\documentclass[12pt,openany]{book}
\pagestyle{plain}
\usepackage[margin=1.8cm]{geometry}
\geometry{a4paper}
\usepackage[parfill]{parskip}
\usepackage{amsmath}
\usepackage{amssymb}
%\usepackage{fontspec,xltxtra,xunicode}
%\newfontfamily{\AR}[Script=Arabic]{Scheherazade}
\usepackage{tipa}
\begin{document}
\textipa{\slshape f@"nEtIks}
\end{document}

\textipa, theIPAenvironment gives correct results to me. – egreg Jul 27 '12 at 07:03\textipa[ss]{...}. – Marian Apr 08 '19 at 13:17