Translate login error message

The two messages you noted are native WP error messages. They would be in the WordPress translation files.

If you’re running a translated version of WP that is complete, then those strings should be included in whatever language pack is being used. (That is part of the reason why WP-Members shifted to using the core WP error messages – it’s far more likely for core WP translations to be updated regularly that for a plugin.)

Those strings originate in wp-includes/user.php in the function wp_authenticate_username_password(). The function is triggered by WP’s authenticate filter hook. The way WP-Members handles login, it runs wp_signon(), which ultimately runs the WP authentication. Those errors are translated when they are added to the error object. When WP-Members is displaying the message, it is getting it from the error object.

So if you’re getting these string untranslated and you are running WP in your language, you may need to look at whether another plugin is causing it. That’s a common WP filter that can be hooked into by any plugin, and I have seen third party plugins replace it with their own authentication.

If you have any plugins that have anything to do with login authentication (including what is through wp-login.php, as that is the exact same process), you should test with them deactivated to see if the untranslated string is being added by another plugin.