Set LANG=C for all unit tests
DateFormatterTest is e.g. checking strings which depend on loclized terms and time formatting, so fails for me when running "make test" where my system has "LANG=de_DE.UTF-8".
I wonder if such settings should not be done upstreams e.g. in ecm_add_test(), by having an optional flag for convenience, given the need for standardized environment is more common. Too bad I need a break from cmake for a while, so this needs someone else to do it ;)