10.2.3 Locating Message Catalog Files
Because many different languages for many different packages have to be
stored we need some way to add these information to file message catalog
files. The way usually used in Unix environments is have this encoding
in the file name. This is also done here. The directory name given in
bindtextdomains second argument (or the default directory),
followed by the value and name of the locale and the domain name are
The default value for dir_name is system specific. For the GNU
library, and for packages adhering to its conventions, it's:
locale is the value of the locale whose name is this
LC_category is always
The value of the locale is determined through
setlocale (LC_category, NULL).
dcgettext specifies the locale category by the third argument.