Living my whole life in Arkansas, US, I'm certain that "if I were" is never used by locals. Instead, phrases like "if I was," "you was," and "they was," have replaced their equivalents in other regions. I've heard these so often that I think it's necessary to ask if they are grammatically correct as a part of a southern dialect. Does their appearance in a certain region as acceptable excuse their application in formal writing? Personally, I indeed believe that anything not found in generic, "accent-free" areas should not be considered correct. But officially within a southern US dialect, are these constructions grammatical?

Liv­ing my whole life in Arkansas in the United States, I’m cer­tain that if I were is never used by lo­cals. In­stead, phrases like if I was and you was and they was have all re­placed their equiv­a­lents in other re­gions.

I’ve heard these so of­ten that I think it’s nec­es­sary to ask if they are gram­mat­i­cally cor­rect as a part of a south­ern di­alect. Does their ap­pear­ance in a cer­tain re­gion as ac­cept­able ex­cuse their ap­pli­ca­tion in for­mal writ­ing?

Per­son­ally, I in­deed be­lieve that any­thing not found in generic, “ac­cent-free” ar­eas should not be con­sid­ered cor­rect. But of­fi­cially within a south­ern U.S. di­alect, are these con­struc­tions gram­mat­i­cal?