This study explores the potential of using a serious game combined with an immersive learning method to support early-stage second language acquisition (SLA). A constructed language inspired by Chinese was designed to serve as a simplified and unfamiliar auxiliary language, enabling a neutral platform for examining language learning without prior language knowledge. Based on this language, I developed Robo’s Language, a 2D dialogue-based video game that contains comprehensible input through environmental interaction, character dialogue, and visual dialogue log—entirely without translation or existing linguistic references. A mixed-method approach was adopted, incorporating both quantitative assessment and qualitative interviews. Ten participants from diverse cultural and linguistic backgrounds completed the demo and participated in the post-game evaluation. Results show that most participants were able to infer and understand a significant portion of the constructed language, with several scoring higher than expected. Many participants can also infer some linguistic rules without any tips. The findings suggest that serious games, when designed with immersive contexts and structured input, have strong potential to enhance engagement and effectiveness in early-stage SLA.