Tradetalk serves the game purpose of allowing a party of Sartarites, Praxians, and Lunars to be able to communicate with each. You only need a minimal skill in Tradetalk to get basic concepts across (“how many moneys for sheep?”) and pretty much everyone can start out with a minimal skill.
There are many lingua francas in the real world. My favorite inspiration is Plain Indian Sign Language, which was used by some 37 different languages in 12 different language families, notably for trading. It was fully formed before the European arrival in the Americas. It enabled a Zuni to be able to trade with a Flathead or a Ojibwa, despite none of these groups even sharing a language family let along any political unity.
