To add language support from the command line, set the pertinent locale facet with the pkg change-facet command. For example, you would use the following command to add support for French as spoken in France.
To install files common for all French locales
# pkg change-facet facet.locale.fr=True
To install files specific to French in France
# pkg change-facet facet.locale.fr_FR=True
You would use the following commands to add support to all available French variants.
To install files common for all French locales
# pkg change-facet facet.locale.fr=True
To install all files specific to all of the French variants
# pkg change-facet facet.locale.fr_*=True