Don't worry. German versions usually have subtitles in half a dozen of languages and very often the original sound is also available. If you give me a link to the version you bought, I can look up the language options on the German website.
Your bigger prob might be the different systems (PAL vs NTSC) and a possible region lock. But neither should matter if you watch the DVD on a computer.
Would it be
this one? It (surprisingly) has no subtitles but an English dolby digital 5.1 version in addition to 3 German ones