Researchers have recently introduced various LexTALE-type word recognition tests in order to assess vocabulary size in a second language (L2) mastered by participants. These tests correlate well with other measures of language proficiency in unbalanced bilinguals whose second language ability is well below the level of their native language. In the present study, we investigated whether LexTALE-type tests also discriminate at the high end of the proficiency range. In several regions of Spain, people speak both the regional language (e.g., Catalan or Basque) and Spanish to very high degrees. Still, because of their living circumstances, some consider themselves as either Spanish-dominant or regional-language dominant. We showed that these two groups perform differently on the recently published Spanish Lextale-Esp: The Spanish-dominant group had significantly higher scores than the Catalan-dominant group. We also showed that the noncognate words of the test have the highest discrimination power. This indicates that the existing Lextale-Esp can be used to estimate proficiency differences in highly proficient bilinguals with Spanish as an L2, and that a more sensitive test could be built by replacing the cognates.