We conducted three experiments investigating in more detail the interaction between the two effects of bilingualism and L1-L2 similarity in the speech performance of balanced and unbalanced bilinguals. In Experiment 1, L1 Mandarin monolinguals and two groups of Hakka and Minnan balanced bilinguals (Hakka: more similar to Mandarin) performed a non-contextual single-character reading task in Mandarin, which required more inhibitory control. The two bilingual groups outperformed the monolinguals, regardless of their L1 background. However, the bilingual advantage was not found in a contextual multi-word task (Experiment 2), but instead the effect of cross-linguistic similarity emerged. Furthermore, in Experiment 3, the Hakka unbalanced bilinguals showed an advantage in the non-contextual task, while their Minnan counterparts did not, and the impact of L1-L2 similarity emerged in both tasks. These results unveiled the way the two effects dynamically interplayed depending on the task contexts and the relative degrees of using L1 and L2.