Taking a memory test after an initial study phase produces better long-term retention than restudying the items, a phenomenon known as the testing effect. We propose that this effect emerges because testing strengthens semantic features of items' memory traces, whereas restudying strengthens surface features of items' memory traces. This novel account predicts that a testing effect should be observed even after a short retention interval when a language switch occurs between the learning phase and the final test phase. We assessed this prediction with Dutch-English bilinguals who learned Dutch Deese-Roediger-McDermott word lists through restudying or through testing (retrieval practice). Five minutes after this learning phase, they took a recognition test in Dutch (within-language condition) or in English (across-language condition). We observed a testing effect in the across-language condition, but not in the within-language condition. These findings corroborate our novel account of the testing effect.