here's another "fun" grep locale oddity:
$ echo HI | LANG=en_US.utf8 grep '^[a-z]'
HI
$ echo HI | LANG=C grep '^[a-z]'
$
apparently en_{GB,US}.utf8 orders a-z like aAbBcC..zZ. $ echo ZI | LANG=en_US.utf8 grep '^[a-z]'
$