In a kickstart file, there is a keyword "langsupport". Here is a
short rundown of various scenarios, just be sure to have only 1
langsupport line in any kickstart file.
When parsing the kickstart file, the first langsupport entry is read
and interpreted, then all subsequent entries are ignored.
langsupport en_US
This installs only en_US (and it becomes the obvious default)
langsupport --default=en_US
This sets your default system language and locale to American English,
but it also makes all other languages available.
langsupport --default=en_US en_US fr_FR de_DE
This will install English as the system default, makes French and
German available, but doesn't install any other languages.
Note that the syntax of language tags for some languages has changed in
the past, especially those with a none-Latin code page, so you may also
have to filter them through your script which breaks up the merged
kickstart file.
As more and more languages are encoded under UTF8, we can expect the
naming of languages and locales to stabilize.
However, parsing only the first langsupport entry and ignoring all
subsequent and conflicting entries is ... undocumented and may
change in the future.
Special thanks to Stefan for his help in clarifying the "langsupport" kickstart keyword.