Showing the Firebase error messages (error.message) in the view results in english error descriptions (e.g. for Authentication errors, if user credetials contain errors).
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Firebase's error message are targeted at application developers, so are in English only. While we'd love to provide them in the same languages as we provide our documentation in, that will never cover all the languages of your users.
So you will have to detect the error in your code, log the error to a central system where you can inspect the problem and then show a localized error message to your user.
As far as I know there is no standardized way of doing that in Angular. But if there is, it'll be unrelated to Firebase.