The last action that should be performed by a language specific file, is
activating it's definitions. Before doing that the macro \originalTeX
should be definined.
\@ifundefined{originalTeX}{\let\originalTeX\relax}{}
Also, the macro \l@ 〈:〉!:}language should be defined. If it hasn't
already been defined, this means that no hyphenation patterns were loaded for
this language.
\@ifundefined{l@dutch}{\addlanguage{dutch}}{}
\selectlanguage{dutch}