The following code processes cleanly under TL2013 and fails with ConTeXt  ver: 2014.02.14 17:07 MKIV beta  fmt: 2014.2.16  int: english/english. I suspect a regression, but I am also open to being told that I am doing things incorrectly.

I also notice that it fails (even under TL2013) if a space is inserted after [#SETUP] in the doTrans intro. I thought that spaces should be allowed in \starttexdefinition -- is this only in the body and not the parameter description?

% macros=mkvi

\showframe


\let\EndTranslation\relax

\starttexdefinition Trans
  \dosingleempty\doTrans
\stoptexdefinition

% The following should work, but fails with current beta
\starttexdefinition doTrans [#SETUP]#TRANSLATION\EndTranslation
  \language[en]
  \doifsomething{#1}{\getparameters[TR][setup=,#SETUP]\TRsetup}
  \noindentation\blank[halfline]
  (\,\ignorespaces#TRANSLATION\removeunwantedspaces\,)
\stoptexdefinition

\starttexdefinition Translation
  \dosingleempty\doTranslation
\stoptexdefinition

% This version works with both Texlive and current standalone beta
\def\doTranslation[#SETUP]#TRANSLATION\EndTranslation%
{\language[en]%
 \doifsomething{#SETUP}%
   {\getparameters[TR][setup=,#SETUP]\TRsetup}%
 \noindentation\blank[halfline]%
 (\,\ignorespaces#TRANSLATION\removeunwantedspaces\,)%
}

\starttext

Translation using \tex{def}{\tex{doTranslation}} works both with TL2013 and current beta.

\Translation[language=en]
  It betrays a slow-witted mentality to pursue the streams, but not to see the sources of things.
\EndTranslation

\blank

Translation using \tex{starttexdef doTrans} fails with current beta.

\Trans[language=en]
  It betrays a slow-witted mentality to pursue the streams, but not to see the sources of things.
\EndTranslation

\stoptext
--
Rik Kabel