This study examines a task that can be applied in a uniform fashion across different languages to compare levels of vocabulary development in foreign language learning. Experiment 1 tested native speakers of Russian and German and demonstrated the basic comparability of the subjects' judgments for both words and nonwords. The results for Russian showed an influence of word length, which can be understood in terms of the Orthographical Depth Hypothesis. Experiment 2 applied the same task to learners of Russian and German and found that learners of Russian had achieved a lower level of vocabulary control than learners of German at comparable language exposure levels. This disadvantage for Russian can be attributed to the novelty of the Cyrillic graphemic system, which restricts the accessibility of written language input at early stages. There was a nonlinear increase over time in word sensitivity, which can be attributed to the increasing contribution of lexical plausibility factors at later stages of learning. Moreover, the lexical decision task appeared to be sensitive to inhibitory effects of concurrently studied languages, as well as to decay due to the lack of regular exposure. Together, these results indicate that the lexical decision task can be a useful tool for the assessment and crosslinguistic comparison of lexical development in foreign language learning.