Hi,

I discovered this bug while answering a question on TeX.SX. Consider:

\define\cyrdash{\dontleavehmode\scale[sx=0.80]{---}}
\unprotect
\setuplanguage
   [\s!ru]
   [
     \c!midsentence=\cyrdash,
     \c!leftsentence=\cyrdash,
     \c!rightsentence=\cyrdash,
   ]
\protect


\setupbodyfont[dejavu]

\starttext
Normal text|<|English

\mainlanguage[ru]
Normal text|<|Russian
\stoptext

The pdf shows:

Normal text—English
Normal text„Russian

Why the quote instead of the emdash. The output is okay is if 
\mainlanguage is set before |<| is used for the first time.

Aditya