This chapter examines the role of common spoken languages in international trade using a structural gravity model. By distinguishing between native (CSNL) and acquired (CSAL) spoken languages, we analyze their impact on trade flows at both the extensive and intensive margins. We find that linguistic commonality reduces fixed and variable trade costs, facilitating communication, trust, and efficiency in trade relationships. These effects are particularly pronounced in the exchange of complex, differentiated goods. Methodologically, we address key challenges, including the endogeneity of language variables and the spatial clustering of linguistic diversity, using robust econometric techniques. Beyond trade flows, we simulate the welfare effects of increased linguistic commonality. Our findings indicate that investments in language education and policies promoting linguistic integration yield substantial welfare gains, benefiting both domestic and international markets. This chapter advances the understanding of language as a determinant of trade and welfare, offering micro-founded insights into how linguistic factors shape economic outcomes. By integrating comprehensive measures of linguistic commonality into a gravity framework, the chapter sheds light on the broader implications of linguistic diversity for global trade, economic policy, and welfare distribution.