An accent was a vocal inflection particular to the people in a specific geographical region.
In both the prime reality and the alternate reality, Pavel Chekov's Russian accent caused him to pronounce v's as w's and vice versa. (Star Trek IV: The Voyage Home and Star Trek, most notably.)
Data's multiple characters in the Ancient West holoprogram exhibited different accents, including western and Mexican. (TNG: "A Fistful of Datas")