Some error messages use the indefinite article:

    "expected a bytes-like object, %.200s found"
    "cannot use a bytes pattern on a string-like object"
    "cannot use a string pattern on a bytes-like object"

but others don't:

    "expected string instance, %.200s found"
    "expected str instance, %.200s found"

Messages tend to be abbreviated, so I think that it would be better to just omit the article.

I don't think that the error message "bad repeat interval" is an improvement (Why is it "bad"? What is an "interval"?). I think that saying that the min is greater than the max is clearer.