That's true - we won't consider anyone without a good command of English. However, as written below, we think the overall communication could get fragmented if there was only one English-only speaking person in the company.
That's definitely understandable, though I guess a bit sad. Does anyone who's not Polish speak Polish? That hasn't been my experience. I've met a few Polish people and seemed such a foreign language to me(doesn't sound like any European or Slavic language I've ever heard). Does it have any related languages whose speakers would be able to pick it up easily?(such as French/Spanish/Italian for example).
Since you're hiring and working remotely doesn't this severely restrict your hiring pool?
Yup, that's true. People from Ukraine, Russia, Slovakia, Czech Republic can easily relate to Polish.
This might be a bit controversial (purely my opinion, not company's) but I think that you'd rather either go full monty and employ 100% multicultural crew or rather stick to a 100% monocultural group. Why? For easier communication.
I recall a situation, working at my previous work, where we hired one guy from South America. His tech side was impeccable, his English needed some brushing up, he's really amiable yet the main problem was people not always switching to English with him around. Not out of malice, some people weren't that comfortable with Eng.
Since you're hiring and working remotely doesn't this severely restrict your hiring pool?