\input regression-test.tex
\documentclass{article}
% Automatic generation of a trilingual language command: languages={de,en,fr}
% with no explicit base name must define \ldeenfr and select the branch for the
% target language, in both the plain and the starred (@n) form.
\usepackage[
  languages={de,en,fr},
  targetlang=en
]{langselect}
\begin{document}
\START
\TYPE{plain=[\ldeenfr{DE}{EN}{FR}]}
\TYPE{star=[\ldeenfr*{d-@1}{e-@1}{f-@1}{X}]}
\END
\end{document}