If the length of user and group name is not constant value, then, we need ngettext support for two strings:

#: ../src/users/group-settings.c:203
#, c-format
msgid "The group name should have less than %i characters for being valid"

#: ../src/users/user-settings.c:293 ../src/users/user-settings.c:298
#, c-format
msgid "To be valid, the user name should have less than %i characters."

Some info is here: http://developer.gnome.org/doc/tutorials/gnome-i18n/developer.html#plurals

Please note that string freeze for the 2.14.x releases starts on 13th February as stated at: http://live.gnome.org/TwoPointThirteen .