Guide to LaTeX (4th Edition) (Tools and Techniques

256 Chapter 11. Multilingual L AT E X
• redefining \originalTeX to be \noextraslang so that the next
language switch will remove those features specific to lang.
11.2 Contents of the language.dat file
As has been mentioned before, with T E X version 3.0 and later it is possible
to store more than one set of hyphenation patterns in the format file.
The counter \language is used to switch between them by setting it to a
different number.
However, there is no standard to dictate which languages belong to
which numbers. If a package were to assume a certain ordering, it would
most certainly function incorrectly at installations other than the one
for which it was designed. The babel system invokes a more reliable
procedure.
During the production of the format by initex (Section B.1.3), the file
hyphen.cfg is input, which in turn reads in language.dat, the only file
to be tailored to the local installation. This file contains a list of languages
to add as well as the name of the file with the hyphenation patterns and
the name of any additional file to be included. It also indicates names of
dialects that use the same hyphenations by prefixing the name with an
equals sign. For example, if language.dat contains
=USenglish
american ushyphen.tex
english ukhyphen.tex
=UKenglish
=british
french frhyphen.tex
german dehypht.tex
ngerman dehyphn.tex
the hyphenation patterns stored in files ushyphen.tex, ukhyphen.tex,
frhyphen.tex, dehypht.tex, and dehyphn.tex are loaded under the
language numbers 0 to 4 respectively, and \l@american, \l@english,
\l@french, \@german, and \l@ngerman are defined as numbers 0 through
4 for use with the \selectlanguage command. Languages \l@USenglish
and \l@UKenglish are synonyms for the current language, in this case 0
and 1, respectively. Similarly \l@british is identical to \l@UKenglish.