Add links:
en_CA, en_GB => en_US
en_AU, en_NZ => en_GB
fr_CA, fr_CH => fr_FR

There are separate links for GB English' and US English' because I
anticipate users of the former to potentially want a thousands_sep of
" " (to match modern British style) rather than ",".

XXX What about en_IE? ISO_8859-15?