This technically goes back into pre-history, so it's out of the scope of this sub reddit, but I can answer this question in the context of Native Americans. The Native Americans of the great plains had a universal form of sign language that was shared by at least 37 oral languages. This allowed different tribes to communicate rather effectively and conduct trade. Aboriginals in Australia also had Manually coded languages, and some Anthropologists argue that sign language predates spoken language. It would be pretty safe to assume that groups of hunter gathers in pre-history had some basic ways to communicate with those outside of their group using hand gestures.
Two things:
This might be better suited to /r/AskAnthropology or /r/linguistics than here.
You might want to specify a time and place.
A common misconception about foragers (which is now preferred to hunter-gatherers because it includes the variety of food-getting activities foragers employ such as fishing and beachcombing) is that one forager band would only rarely encounter another one; that is, that people would be living in a landscape where other people would be very rare.
However, forager life, like all human life, is very social. Your own band may be only 20 or so people, but you may know and have contacts with hundreds of people. This would be due to a lot of things; forager bands go through frequent splits and mergers and different bands will generally join together for part of the year when resources are concentrated. Among San people in the Kalahari, people would disperse in small groups in the summer and then aggregate in large groups around water holes in the winter. Since people wouldn't always aggregate at the same water hole every year, they could meet people from far away.
If you're specifically asking about groups who spoke different languages, well, language groups are much more fluid for foragers. People could speak many languages and move from one group to the other. For example, the San are comprised of many different language groups. In the Northwest Kalahari, there's two groups in particular: !Kung speakers such as the Ju/'hoansi and Nharo speakers. !Kung and Nharo are as closely related to each other as Spanish and Chinese, but they've exchanged a lot of vocabulary and have the same set of names (San people tend to have only ~20 names for each sex). In fact, in Namibia Nharo people often call themselves Ju/'hoansi. They're perfectly able to communicate with each other.
Basically, for foragers, there generally aren't the sharp group boundaries that people think of as "natural" for humans.