In my setting I'm devising, Terrans (us) were kidnapped and brought to a new handful of solar systems across the galaxy where several other "nations" exist of various alien species.

I'm using GURPS 4e.

In GURPS you have cultures like Western Culture or Eastern Culture, etc.

BUT. These are based on Earth norms, regions, etc. I want to differentiate them not only between Terran cultures but in a potential sea of "non human" cultures.

Suggestions?

For the earther/terran/dirtmen exiles it seems like there is two ways to go.

One: use a name chosen by others to describe the earthers. In this case the name might be kind of meaningless from an earth perspective e.g. two-leggers or mouths-on-heads if that is unusual.

• Upside - human cultures get weird, possibly humorous names.
• Downside - your players will have a harder time recalling what culture goes with what name.

Two: use a name that comes from the culture that came from earth. So if the culture is based on feudal Japan maybe it is whatever the Japanese word is for the people or is related to Japanese culture from the exiles place of origin...People of Amaterasu, People of the Rising Sun, even the Lost Ones, if translated into a Japanese phrase might sound cool, something like that, maybe something based on Ronin the masterless samurai since these people were cut adrift from daimyo, clan, and home.
Similarly Western culture is the specific place they are from like France or even just a province like Languedoc or Brittany or the people's thereof. For France one could revert to names of the earlier Gallic tribes.

• Upside - connects the name to the culture in a way that may be meaningful and easier to remember for you and your players.
• Downside - doesn't necessarily highlight the stranger in a strange aspect of people from different earth (places or times?) since it may seem like the home culture.

The theme seems a little bit like the time displacement stories by Harry Turtledove (Videssos), David Drake (Ranks of Bronze which has Romans kidnapped by Aliens to fight as mercenaries), and Eric Flint's 1632 series. It might be worth taking a look at how those authors refer to their displaced groups. Psychologically it would seem like people are going to want to hold onto their old identities if they can. If nothing else, as a form of resistance and remembrance.

Sky's the limit, and I need way more setting background knowledge and what effect you are trying to go for before I could even attempt.

I mean, humans with their whistling, flapping meat sounds might end up on a planetary atmosphere that craps on our Terran-evolved form of communication. And given various tech levels, several likely alien with who knows what conversion capacity, it could be based on anything from scintillating colors to exotic smells — or time-lapsed interpretive dance. We're already boggling our own mind scrambling to decipher the mechanisms plants and fungi use to sense and then communicate amid their environment; you're asking for a universe of possibilities if we just pattern things off of known life in our world, let alone elsewhere.

Give limits. You need them.