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