I spent two hours digging through registry keys and config files to save you the headache. If your ACDSee language is stuck or changed unexpectedly, here is the fix that actually works:
If ACDSee suddenly displays the wrong language (menu items, dialogs, or messages), common causes are wrong application language settings, corrupted configuration files, an update/installer choosing a different locale, or OS locale/language settings interfering. Fixes include switching the language in ACDSee preferences, reinstalling with the correct language, resetting app settings, or editing/clearing configuration files. acdsee language change fixed