Make sure you've correct localization set in Battle.net game options, not just in-game options of SC2.
Also you could try to force change of Editor options by overriding relevant config key in regedit
reg add "HKCU\Software\Blizzard Entertainment\StarCraft II Editor\Preferences" /t REG_SZ /v Locale /d enUS /f
I have no idea if it will work. But it should be done while editor is off. At next launch it wil either start downloading new localization files, or revert back to previous settings..
Previously known as: SomeoneTookMyNameTT