relationship.py: Fix not registering "en_GB" as english.

Also replace diagnostic print with proper logging.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21279 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
grampslocale.py: Protect against C.UTF-8 not being an installed locale on Linux.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21280 4ae1f11a-8b86-4847-b8af-ab372f36d1fd