Addon Packages (langpacks)
The idea behind "langpacks" is to divide translations and language specific content into subpackages in the case that the size of translations is enormous or the package is part of a core image that should be minimal.
Packages that exist solely to contain additional language translations or content must be named in the syntax <pkgname>-langpack-<langcode>, where <pkgname> is name of the package the langpacks belong to and <langcode> is a valid language code from /usr/share/xml/iso-codes/iso_639_3.xml or from /usr/share/i18n/locales/. Specifically, the langcode value used in the package name must match the langcode identifier used in the directory path by upstream for the language translation files.
The langpack ecosystem does not need any procedural logic in form of plugins. Instead it takes advantage of the weak and rich dependency features provided by RPM. The necessary dependencies are computed by package manager (DNF or PackageKit) so it's crucial to define following relation into the langpack definition in the spec file using the Supplements: tag as follows:
Supplements: (%{name} = %{version}-%{release} and langpacks-<langcode>)
Example
Suppose you have a package with following spec file:
Name: php-horde-Horde-Perms ... %files -f Horde_Perms.lang /usr/share/pear-data/Horde_Perms/locale/ ...
In order to create langpacks for each language (/usr/share/pear-data/Horde_Perms/locale/<language>/LC_MESSAGES/Horde_Perms.mo translations), you would need to change the spec file for such language. The snippet below shows the definition of one langpack for bs language by altering the spec file defined above.
Name: php-horde-Horde-Perms ... %package langpack-bs Supplements: (%{name} = %{version}-%{release} and langpacks-bs) %files langpack-bs /usr/share/pear-data/Horde_Perms/locale/bs/LC_MESSAGES/Horde_Perms.mo
%files ...