The \lefttoright and \righttoleft commands set the paragraph direction
when you use the commands at the begin of a paragraph.
\setupwhitespace[line]
\starttext
\input ward
\righttoleft
\input ward
\lefttoright
\input ward
\stoptext
Still there is no need for \righttoleft because you can use the normal
alignment commands {\setupalign and \startalignment) to change the text
direction.
\setupwhitespace[line]
\starttext
\input ward
\startalignment[righttoleft]
\input ward
\stopalignment
\input ward
\stoptext
Wolfgang