Ottoman Turkish (Arabic letters)

Using XeTeX or LuaTeX, with Unicode input and a font with proper support (e.g. Scheherazade), things should be as simple as:

\documentclass{article}

\usepackage{fontspec}
\usepackage{bidi}

\newfontfamily\ottoman[Script=Arabic]{Scheherazade}

\begin{document}
\begin{RTL}
\ottoman
لسان عثمانی
\end{RTL}
\end{document}

Using LaTeX you can use arabtex with the setfarsi option. You will need to use transliterations for the input (much like pinyin in Chinese). Here is a minimal:

\documentstyle[12pt,arabtex]{article}
\parindent=0pt 
\begin{document}
\null \vskip -2cm
\setfarsi \novocalize \Large
%
\begin{arabtext}
a b c d e f g h  \\
0123456789\\
donald knuth pasha\\
\end{arabtext}
%
\testoutput
\end{document}

Would appreciate it if you can provide a good paragraph for testing, as I don't speak the language (know a bit of Turkish and Arabic). The output has its own beauty though.

Depending on “how much” text you need in that language, you can set small pieces of text just setting:

\usepackage{fontspec}
\newfontfamily{\A}{Geeza Pro} %or any other font

Now you can insert thus:

{\A السلام عليكم}

And compile with xelatex or luatex.