Herein we present electrophysiological evidence of extremely rapid learning of new labels in a second language (L2) for existing concepts, via computerized games. However, the effect was largely constrained by crosslinguistic grammatical gender congruency. We recorded ERPs both prior to exposure with the L2 and following a 4-day training session. Prior to exposure, no modulation of the N400 component was found as a function of the correct Match vs. Mismatch of audio presentation of words and their associated images. Post-training, a large N400 effect emerged for Mismatch compared to Match trials, but only for trials on which the L2 words shared grammatical gender in the learners' L1. Behavioral results showed that all L2 words were learned equally as well, independent of gender congruency across the L1 and the L2. The results demonstrate that crosslinguistic grammatical gender congruency influences lexical activation during the initial stages of establishing a new L2 lexicon