Introduce wp_load_translations_early(), which can be used before the locale is...

Introduce wp_load_translations_early(), which can be used before the locale is properly loaded in order to translate early error strings. Internationalize setup-config.php -- translators no longer have a reason to modify this file. fixes #18180.

git-svn-id: https://core.svn.wordpress.org/trunk@19760 1a063a9b-81f0-0310-95a4-ce76da25c4cd