In an English work, can a non-English source be cited even if there exists an English translation?
There are two things to address here. First, relax. The exact sources you are citing in a writing sample for an MA program are NOT what the admissions decision will be based on. It is unlikely anyone is going to check up on your citations and even if they do, they are not going to care.

The second thing is, it is generally best to use the original, untranslated source. When the original source is not in a language you are proficient in, using a translation is reasonable. If you are writing in English and need to use a translation, then using the English translation is best, unless there is a compelling reason not to. In the future, you may want to work with English translations, but again for a writing sample, no one is going to care.