Expansion of command for language in otherlanguage environment

Question

I wish to keep the language in a command

\newcommand{\testlang}{english}
\begin{otherlanguage}{\testlang}
 ...
\end{otherlangauge}

However, \testlang is not expanded, and i get the error

! Package babel Error: You haven't defined the language testlang yet.

I've seen many tricks related to macro expansions, but I don't understand them well enough to know how to apply them in this scenario.

Answer 1

You can expand the argument manually using the following techniques. The easiest thing would be to define your own wrapper environment.

% Expand the argument once:
\newenvironment{Otherlanguage}[1]{%
  \expandafter\otherlanguage\expandafter{#1}%
}{\endotherlanguage}


% Alternative: argument is fully expanded
\newenvironment{Otherlanguage}[1]{%
  \begingroup
  \edef\temp{\endgroup\noexpand\otherlanguage{#1}}%
  \temp
}{\endotherlanguage}

% usage    
\begin{Otherlanguage}{\testlang}
 ...
\end{Otherlangauge}