Should REST API return UI friendly error messages?

Question

Today I had a discussion with one of my colleague for REST API Schema, the consumer in this case will be a mobile app(android & iOS). While discussion my colleague raised a request that the API should return a mobile user friendly error message and that too with multi-lingual support.

Here is what I proposed.

For an error in the backend, example a 400

{
  "errors":[
    {

      "username": "Invalid username",
      "code": 453
    }
  ]
}

What he was suggesting was to return a more human/app friendly error message with multi-lingual support:

{
  "errors":[
    {

      "username": "Entered username is incorrect, please try again",
      "code": 453
    }
  ]
}

Now my view on this was that this will make the REST API tightly coupled with the mobile App. Ideally the translations & readable error messages need to be handled in the mobile app itself.

After lot of to and fro discussion,I thought of asking this to the dev community, on what should be the approach on this?

Answer 1

Am of the opinion that every api should provide reasonable, well-formatted error messages. What's the alternative, doing several checks when there's an error.

I've seen places where they use numbers as codes for different kinds of errors. The frontend then has to do a check each time they make a request that returns an error. Which then leads to similar logic being implemented across multiple application that all communicate with the same endpoint.

And as to the claim to tight coupling of the backend with the consumer,

{
  "errors":[
    {

      "username": "Entered username is incorrect",
      "code": 453
    }
  ]
}

is better and doesn't tie itself with any of its consumers.