This cumulative dissertation investigates features of sociolinguistic variation in spoken English by non-native humans and agents. It presents a thorough summary and systematization of previous research on Chinese English, a quantitative analysis of the Chinese English vowel spaces of speakers from Guangdong, Guangxi and Yunnan, a quantitative analysis of durational variation of speakers from different inner, outer, and expanding circle varieties of English, and a study of sociophonetic variation by a pedagogical agent. Furthermore, the thesis proposes a linguistically based quality metric for text-to-speech systems.