The indefinite article – does local pronunciation change when I should use a/an [closed]

I have a question about how different pronunciation of words and how this affects the use of indefinite articles.

My example is the technical abbreviation URL, meaning "uniform resource location". A common way to pronounce it is "you-are-ell", and to use the indefinite article a because of the consonant "y". -- Which is correct — a URL or an URL?

However, since it is an abbreviation, I have always pronounced it word-by-word "u-are-ell", and I have used the indefinite article an with this word.

I would like to extend this question to any word that have a different pronunciation as there are many different dialects.

Is it accepted to chose the indefinite article (a or an) based on how you pronounce a word?

Regardless of dialects, there will tend to be one "official" pronunciation of any word, and you should base your decision on this.

I don't actually understand what the difference in pronunciation between "you-are-ell" and "u-are-ell" would be: saying that you pronounce "U" as "u" is totally redundant and doesn't tell us anything.

If you are speaking, rather than writing, you could use "a" or "an" depending on how you pronounce it, but I'd still recommend pronouncing it in the "conventional" way, just for the sake of clearer communication.