"I have an accent" as a kind of shorthand for "I have a non-standard accent" is in theory fine, since most people know what you mean.
The reason I pointed it out, though, is because the reverse direction - "you have an accent, which is why I don't understand you" - especially when directed at actual native speakers implies (even if not intended) some sort of deficiency on the part of the interlocutor.
The reason I pointed it out, though, is because the reverse direction - "you have an accent, which is why I don't understand you" - especially when directed at actual native speakers implies (even if not intended) some sort of deficiency on the part of the interlocutor.