I can't figure out how to translate this
对我来说，北方人的口音和语速makes it difficult for me to understand them.
What's the best way to say this without losing any of the above meaning and structure?
A English to Chinese translation of your sentence:
But the sentence sounds very translated. A more Chinese way can be:
(I don't understand the northern Chinese very much, because the northern men have accents, and they speak quicker.)
The sentence I give is closer to the Chinese thinking. Note that in your sentence, you use
北方人的口音和语速 as the subject. However, it sounds unnatural to have subject other than
我 when you are talking about your feeling. (but it would be OK if your sentence is to be written down)