Amazon Cognito: Translation of Error Messages in Managed UI

You're correct in observing that not all error messages in Amazon Cognito's Managed UI are fully translated, even when you've set the language to German. This is a known limitation of the current implementation.

While Amazon Cognito's Managed UI does support localization for various languages, including German, the translation of error messages is not comprehensive. Some error messages, particularly those related to authentication failures or input validation, may still appear partially or fully in English.

Unfortunately, at present, there isn't a direct way to customize or fully translate these error messages within the Managed UI. The Managed UI provides a standardized authentication experience with limited customization options, and modifying the error messages or their translations is not currently possible.

If having fully translated error messages is crucial for your application, you might need to consider alternative approaches:

1. You could implement a custom authentication UI where you have full control over the login experience, including error message translations.

2. You could use the Amazon Cognito API directly to manage the authentication flow, which would allow you to handle and translate error messages in your application code.

It's worth noting that AWS regularly updates and improves its services. While this limitation exists in the current implementation of Managed UI, it's possible that future enhancements might address this need for more comprehensive translations. It's advisable to keep an eye on AWS documentation and announcements for any updates related to this functionality.

In the meantime, if this issue significantly impacts your user experience, you may want to consider reaching out to AWS support to provide feedback on this limitation. They might be able to offer more specific guidance or consider it for future improvements to the service.

Sources
Displaying error message in Cognito managed login sign-in page | AWS re:Post
User pool managed login - Amazon Cognito
Cognito Managed Login doesn't seem to support login_hint | AWS re:Post