Some of the language-specific files introduce one or more characters
that are special in some way. Such characters have to be
added to \dospecials (and \@sanitize too for LATEX)
whenever their special meaning is activated. But, they may have to be
removed again when another language, which doesn't use them, is in
effect.
To this end two new control sequences, that are meant to be used in
the language-specific files are introduced. They are
\babel@add@special and \babel@remove@special and perform
the necessary tasks.