The language switching mechanism contains a couple of hooks for the developers of language-specific document-style options.
First of all the macro \originalTeX should be defined. Its function is to disable special definitions made for a language to bring TEX into a `defined' state. A language-specific document-style option might, for example, introduce an extra active character. It would then also modify the definitions of \dospecials and \@sanitize. Such an option would then define a macro to restore the original definitions of these macros and restore the extra active character to its normal category code. It would then \ let \originalTeX to this `restoration' macro.
To enable the language-specific definitions three macros are provided in the switching mechanism, \captions 〈:〉!:}language, \date 〈:〉!:}language and \extras 〈:〉!:}language.
The macro \captions 〈:〉!:}language should provide definitions for the macros that replaced the hard-wired texts in the document style and the macro \date 〈:〉!:}language should provide a definition for \today. The real fun starts with the macro \extras 〈:〉!:}language. This macro should activate all definitions needed for 〈:〉!:}language.