As an amateur interpretation, I'd say "Within any range or circumstance that you can communicate with it".
The Empathic Link ability seems to be the main way for a witch to actually communicate with a familiar. It's fairly unique to familiars, always achieved at first level, and familiars learn it before any form of speech despite reasonable intelligence. Unless your witch/arcanist roleplays out some sort of ritual with their usual spell prep, I'd argue the answer is "within 1 mile".
Only other answers seem to be: "in direct contact" which no evidence shows, some arbitrarily decided distance by your GM, or within speaking distance (if one argues that the Familiar actually learns your language, despite not being able to speak it itself).