Appreciating the humor in jokes involves incongruity-detection and resolution, which requires good language skills. Foreign language comprehension is challenging, including interpreting words within their sentence context. An implication is that jokes in a foreign language will be more difficult to understand and therefore probably less humorous, compared to native language jokes. To study this question while preserving humor across translations, jokes were selected from Turkish and English websites to minimize language play and cultural references. Turkish university students rated both Turkish and English jokes for humor. Humor for foreign language jokes was positively correlated with ease-of-understanding of specific jokes and also by the individual-differences characteristics of English proficiency and likely career investment (e.g., preparing for a future career as English teacher or translator). We propose the proficiency X investment theory: Foreign language jokes will be experienced as funnier than native language jokes when proficiency levels are high ( ranging from good to excellent) and bilinguals have a high level of L2 investment. When proficiency levels are only adequate, and without special investment in L2, native language jokes will be evaluated as funnier than foreign language jokes. With intermediate proficiency and investment, jokes can be experienced as similarly humorous in the two language. Important in this pattern is the proposal that weaker L2-proficiency can trade-off with language investment to bolster L2 humor appreciation.