Upgraded one of WP installation to the latest release and suddenly admin area localization stopped working (theme is translated so public area does not use translation).
1) define(LANG) whatsoever in wp-config is present and defined;
2) locale files .mo and .po are present in wp-content/languages;
3) all locale file are in proper case (lowercase_UPPERCASE 2-letter symbols);
What gives?
Prirt to update everything worked perfectly.
MBString settings are
Multibyte Support enabled
Multibyte string engine libmbfl
HTTP input encoding translation enabled
Multibyte (japanese) regex support enabled
Multibyte regex (oniguruma) version 4.4.4
Multibyte regex (oniguruma) backtrack check On
Directive Local Value Master Value
mbstring.detect_order no value no value
mbstring.encoding_translation On On
mbstring.func_overload 0 0
mbstring.http_input pass pass
mbstring.http_output pass pass
mbstring.internal_encoding no value no value
mbstring.language neutral neutral
mbstring.strict_detection Off Off
mbstring.substitute_character no value no value