This study investigates definite articles in specific and generic subject nominals in Italian spoken by adult simultaneous bilinguals (2L1ers) and second language learners (L2ers). The study focuses on plural and mass DPs, in which German and Italian differ. The aims are to (i) compare acquisition outcomes between the weaker and the stronger language in 2L1 acquisition, (ii) see in a comparison with L2ers whether the phenomenon under investigation, which is typically acquired late (after age 6;0), lacks age of onset effects, and (iii) discuss predictions for the directionality of cross-linguistic influence. Twenty German–Italian 2L1ers and 15 advanced L2ers of Italian with German as their native language were tested in an acceptability judgment task and a truth value judgment task. The results show clear differences between Italian as the weaker and as the stronger language in 2L1 acquisition, and similarities between Italian as L2 and as the weaker language in 2L1 acquisition.