Multiple language barriers.
I speak a little Spanish. Not a lot, but I can usually get basic concepts across.
I do not know sign language, beyond one or two very simple phrases. I can't "get by" in it.
A few months ago, I had a traffic stop in which the driver, a Spanish speaker, was deaf.
My daughter had started drawing in my pocket notebook when she found it on the table while I was doing laundry. I found it in her possession, and confiscated it, because the contents are not her business. (Mostly data without actual connection to specific charges, but still, that's mine.) I found part of the conversation that I had had with the driver when I issued the citation, in the notebook, which I attach here:
It's handy having access to Google Translate in your patrol car, too.