This dissertation uses the Conceptual Blending Hypothesis from the socio-cognitive method presented and refined by Kecskes (2002, 2004, 2007, 2010, 2020) to explain how the lexical choice of bilinguals differs across sociocultural situations. Quantitative (lexical density, lexical diversity, and lexical sophistication) and qualitative (lexical concepts) processes demonstrate this variance. Hence, the thesis shows the interplay between two aspects of the bilingual's word choice, namely conceptualizing and selecting words in the linguistic system, which influence word choice in context (i.e. individual words via words used in essay writing). It is hypothesized that a conceptual blending of the sociocultural loads of the first language and those of the second language (L2) during the conceptualization process influences the formulation and selection of lexical items or words in a target context. 108 students participated in this study, including 72 sequential Chinese-English students from two parallel classrooms at institutions located in the Northeast of the United States and China. In addition, 36 English native-speaking students studying in the same program in the USA were recruited as a baseline group. Ten socioculturally distinct concepts were selected for a conceptual elicitation task (containing [1] individual concept's semantic elicitation, [2] pragmatic contextual and emotional elicitation, and [3] word associations) and an essay employing those concepts and their lexicalized words in English. Data analysis also shows that conceptual blending in synergic concepts can display varied degrees of blending that may affect on-time lexical selection in the actual situational context, which could result in a "third-space" conceptualization and deviational idiosyncratic word choices. The key findings are as follows: (1) during conceptualization (pre-verbal messages), conceptual blending in synergic concepts was detected in all experimental concepts, starting with domineering L1 socio-cultural conceptualization, through dominantly assimilating into L2 conceptualization to deviational conceptualization from both L1 and L2 conceptualization; (2) the locations where the conceptual socialization takes place (using English as a foreign language in native culture versus English as a second language in the target culture) weakly affects or does not affect the reconceptualization of a concept at all; (3) in formulation (formulator), under the influence of synergic concepts, the cognitive saliency of word sequences of two bilingual groups deviates from each other, and the monolingual groups; (4) at the phase of articulation (articulator) in essay writing, pre-verbal synergic concepts (conceptualizer and formulator) are lexicalized into natural collocations or lexical idiosyncrasies that are prominent in the conceptual socialization of bilinguals living in the target L2 culture. These idiosyncrasies are lexicalized from their synergic concepts and stronger conceptual blending when conceptually blending into the target culture. Indeed, bilinguals in the USA have statistically significantly more lexical idiosyncrasies than subjects in China. Furthermore, due to the fact that their lexical density, diversity, and sophistication are comparable to those of monolingual Americans, typical lexical complexities do not distinguish bilingual students in the United States from monolingual Americans, as they do in bilinguals living in China, while lexical idiosyncrasies could be included to help depict their lexical abilities. (5) Lastly, lexical density, diversity, and lexical idiosyncrasies may be utilized together to highlight lexical complexity and differentiate bilingual subjects in terms of their bilingual pragmatic competence, although text lengths and lexical sophistication cannot. Individual characteristics, such as metapragmatic awareness and holistic translanguaging in conceptualization and lexicalization, might guide bilingual students' lexical choices towards a specific audience. The study provides novel insights into the dynamics involved in bilingual language usage and bilingual pragmatic competence, as demonstrated by the conceptual and linguistic evolution of bilingual learners' vocabularies as represented by word selection. The pedagogical implications of the study are also addressed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]