My view is that apis should simply return a number when an error occurs. The vendor should supply a list of error codes to its consumers, translated into as many languages as necessary. The developers who are consuming the api can then determine how best to present the error to its end users. A set of error numbers is tied to the version of the api that is being consumed so there should be no surprises.
In other words, if a set of people don't understand the message, make sure that no one understands the message (not even the people that normally just press the Google Translate button).
Is that what you're saying? Or did I misunderstand you?
