Previous studies have shown that the disruptive effect of task-irrelevant speech on short-term memory can be attenuated by providing intelligible foreknowledge of the specific distractor materials. However, it is yet unclear whether this benefit results from familiarity with the sound of forthcoming distractors or whether it is due to reduced interest in the semantic content or syntactic structure of the irrelevant utterances to be presented, thus reducing stimulus-specific attentional capture. This was tested in the present study by providing literal foreknowledge of task-irrelevant spoken sentences either in the same or a different language (German or English). Crucially, half of the participants (German sample) were familiar with both languages while the other participants (UK sample) were unfamiliar with one of the languages. Participants were instructed to listen to the sentences during the foreknowledge period and to ignore the sentences during the memory task. It was found that both German and English foreknowledge reduced auditory distraction in German participants, when presented with the same irrelevant speech materials during the memory task. In contrast, the UK sample benefited only from English foreknowledge presented prior to English irrelevant speech. These results suggest that foreknowledge reduces the degree of attentional capture elicited by semantic or syntactic properties of irrelevant speech, whereas it seems to have no effect on the distraction due to the acoustic properties of the distractor sound.