The DIBT program is very comprehensive, and a very good level of English knowledge (C1 level) is required. When we review applications, TOEFL/IELTS exams are generally used as an English level benchmark. However, we also accept “other proof” of English proficiency, and the selection committee do look at applications on an individual basis. If your previous studies have been in English, this should be sufficient. Please make sure you clearly state this in your application.
For more information on English-language competence requirements of WU, please see the following LINK.