There seems to be some limitation (or bug) in right-to-left (r2l) alignment, when used alongside linenumbering. Consider the following:
\setuppapersize[A6] \starttext \showframe
\section{Incorrect} \startlinenumbering \startalignment[r2l] Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque molestie dictum quam non congue. Integer ut dolor vel mi vestibulum molestie vel et nulla. \stopalignment \stoplinenumbering
\section{Correct} \startalignment[r2l] Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque molestie dictum quam non congue. Integer ut dolor vel mi vestibulum molestie vel et nulla. \stopalignment
\stoptext
The RTL alignment works correctly on its own. However, when you introduce another factor — here, linenumbers — the RTL alignment is ignored. Perhaps this linked to the problem with of RTL footnotes being discussed here: gmane.comp.tex.context/92113 http://article.gmane.org/gmane.comp.tex.context/92113? Best wishes, Talal