This study compared how first-language Spanish and German speakers learn English vowels via computer-based auditory training. Spanish has fewer vowels than German, and thus Spanish speakers may have more unused room in their vowel space for new category learning. However, our results demonstrated that Germans improved twice as much (20 percentage points) as Spanish speakers (10 percentage points) following 5-sessions of training on English vowels (high-variability identification with feedback). The results suggest that the large first-language vowel inventory of German speakers facilitates rather than interferes with new learning.