Comment 3 for bug 1491066

Test case:
# locale-gen et_EE.UTF-8
# echo _abcdefghijklmnopqrstuvwxyz_ | LANG=et_EE.UTF-8 LANGUAGE= LC_ALL= sed 's/[a-z]//g'
_tuvwxy_
# echo _abcdefghijklmnopqrstuvwxyz_ | LANG=et_EE.UTF-8 LANGUAGE= LC_ALL= sed 's/[[:alpha:]]//g'
__

I.e. the locale needs to be generated before it's functional,
and LANGUAGE and LC_ALL need to be unset in order for LANGUAGE to take effect.

Note that `tr` seems unaffected, maybe its developers are automatically replacing [a-z] with [[:alpha:]] internally.

I think that any occurrences of [a-z] in the code should be fixed whether we also decide to use LANG=C.UTF-8 or not.