I would say that rather than saying ‘in [the] [accent]’, one should say ‘with an [accent]’, for example:
‘I speak with a standard southern British accent’.
Thank you! Are there other cases where "the" would be used? For example:No: I would use "a".
I speak with a standard southern English accent.
I'd assume it's what's generally known as "Received Pronunciation" but we don't normally refer to that as an 'accent'.I don't know what a 'standard accent' means but we would say southern English not British. Speaking 'standard English' to me implies a 'standard' accent.