Many models of speech production recognize, despite their differences, that there are three main stages of speech planning: the formation of the concept to be conveyed; the retrieval of phonological representations; and the articulation of the planned speech (Stemberger, 1985; Dell, 1988; Roelofs, 1997; Levelt et al., 1999). One of the debates in the last two decades is what constitutes as the primary planning unit in cross-linguistic online speech production during the phonological encoding stage. The present study aims to shed further light on the issue by investigating whether the primary processing unit is universal and to what extent it is determined by one's language background. We explore this question with bilinguals speaking two different types of languages (Germanic and Sinitic). Further, with the use of ERPs, we investigate the neural activation pattern of the phoneme underlying the presence or absence of behavioral effects which existing debates on primary processing unit have mainly relied upon. In the following, we first introduce the existing literature on Germanic languages which suggested the phoneme to be universally activated in all languages, which is followed by a description of behavioral research in Sinitic languages that challenges this universality view and suggests that the planning unit is language-specific. We then discuss (1) how understanding processing mechanisms of bilinguals with different language backgrounds may shed light on the issue, and (2) how ERPs would give us more insight into the activation pattern of segmental information.