"She spoke in broad Yorkshire dialect." — Why is "a" not used here? — I mean: "She spoke in a broad Yorkshire dialect."

Question

an example from "Extra Examples" on oxfordlearnersdictionaries.com:
(1) She spoke in broad Yorkshire dialect.

As far as I understand, "dialect" in (1) is uncountable since it's used without an article.
But why is it possible to use "dialect" here as an uncountable noun?

"Dialect" has two extra words before it: "broad" and "Yorkshire". These words imply there are different dialects: a non-Yorkshire dialect, a broad Yorkshire dialect and a non-broad Yorkshire dialect. That is, we can count these dialects. Therefore, the attributive words "broad" and "Yorkshire" make "dialect" countable and so it must have an article.
Why is my logic wrong?

my variant:
(2) She spoke in a broad Yorkshire dialect.
Is (2) correct?
If not, then why not.
If it is, what's the difference between (1) and (2)?

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britannica.com:
(3) They speak a southern dialect of French.

my variant:
(4) They speak southern dialect of French.
I thought (4) was incorrect but after seeing (1), I began doubting: maybe (4) is correct as (1) because to me, "broad Yorkshire dialect" and "southern dialect of French" are quite similar constructions in terms of countability.

Is (4) correct?
If not, then how can (1) which is similar to (4) be correct?
If it is, what's the difference between (3) and (4)?

Answer 1

Your interpretation isn't quite right. Broad, when used of an accent or dialect, is a measure of 'strength', so there isn't a sharp distinction between a 'broad' and a 'non-broad' dialect.

Yorkshire is a big county and there are regional variants in the accents of Yorkshire people, so it would be possible to speak of 'a Yorkshire dialect'. However, a person from southern England might not be aware of these differences, just recognise that the speaker comes from Yorkshire, has a strong accent and uses some words typical of the region. They say She spoke in broad Yorkshire dialect as they might say She spoke in French.

Whether you choose to speak of dialect as countable or uncountable is not affected by the use of adjectives to describe it.

Answer 2

Note that English determiners ("a", "the") are different in Broad Yorkshire Dialects.

So if the speaker/writer was influenced by the dialect they were describing, (as is more often the case for spoken grammar: written grammar tends to be more formal), they might drop the "a", either in imitation, or to be indicative.