The current study aimed to gain insight into the nuanced challenges that Vietnamese learners encountered due to the interference of their native linguistic structures and norms. This qualitative study explored the experiences of Vietnamese learners in acquiring English, focusing on the influence of negative L1 transfer. This study focused on the influence of negative transfer from their first language (L1) by drawing upon in-depth interviews and observational data from a group of Vietnamese university students. The results showed that despite exhibiting high levels of motivation and enthusiasm for learning English, Vietnamese learners struggled with the shadows of L1 interference in areas such as pronunciation, syntax, and idiomatic expressions. The tonal nature of the Vietnamese language led to intonation patterns in English that deviated from native norms. Direct translations also contributed to unidiomatic English, indicating a deep influence of L1 thought patterns. Additionally, cultural contexts embedded within the Vietnamese language presented challenges, as some concepts and expressions lacked direct English equivalents. Although students faced various obstacles, they utilized a variety of adaptive techniques to lessen the impact of negative transfer. These techniques included code-switching, peer correction, and self-reflection. The study emphasized the significance of recognizing and comprehending the significant role of L1 when creating English language educational programs and teaching techniques for Vietnamese students. By illuminating the specific challenges and adaptive strategies of these learners, educators could personalize their approaches, leading to a more comprehensive and efficacious language-learning atmosphere.