This study investigates variations in English short vowel sounds and their correspondences within the context of Southern Thailand, focusing on how these variations may affect intelligibility and comprehensibility in spoken English. It also examines the interplay between speech perception and production, focusing on the impact of mother tongue interference (MTI) and language contact (LC). A group of 88 tertiary students whose native language is either the Southern Thai dialect or the Standard Thai language was examined. A questionnaire and tests were employed to explore the correspondence and to assess speech perception and production. The descriptive statistics and post hoc test for one-way ANOVA results indicated that MTI and LC affect the pronunciation of English words, especially the vowel /e/. Furthermore, a new vowel sound correspondence was observed. Cross-tabulation analyses revealed comparable effects of MTI and LC on perception and production abilities. Specifically, speech production tended to mirror perceived sounds, and this effect resulted from MTI and LC. The study highlights the impact of MTI, LC, and vowel variation on English pronunciation among Southern Thai students.