According to the US Department of State, a native English speaker can learn Spanish in about 600 h, but would take four times as long to learn Japanese. While it may be intuitive that similarity between a foreign language and a native tongue can influence the ease of acquisition, what is less obvious are the specific cognitive and emotional processes that can lead to different outcomes. Here, we explored the influence of cognitive strategies and affective states on native English speakers' ability to learn artificial foreign words that vary in their similarity to the native language. Explicit word learning strategies were reported more often, and were more effective for learners of a more similar language, and cognitive strategies were especially helpful for learners with lower moods. We conclude that language similarity, strategy, and affect dynamically interact to ultimately determine success at learning novel languages.