Writing Advice

Pardon me, but can you spare some advice on writing the other?

imageI am currently working on a short story set in the early to mid 20th Century in which all the characters are from the South.

My predicament is with whether to write the dialogue as they would have spoken based on their generation and geographical location or to write all the conversations in plain English, leaving accents and particular pronunciations out of the dialogue.

One of my characters is a former slave who resides in Georgia in the 1940s. Expectedly, he would have a particular vernacular for that culture and region in that particular time period.

Is writing dialogue in plain English acceptable or is it a must that I craft the dialogue to fit the expected language of the character?