The approach to language in Star Conquest, like so much else in the game, finds its origins in the "golden age" of science fiction during an era of space age optimism. It was supposed by authors like Isaac Asimov that humanity would naturally unify and come to speak together in a universal language like Esperanto, an artificial language created in 1887 and designed to be easy to learn and speak.
In the Star Conquest timeline, in the year 2153, the United Nations had already been collectively representing the wealthiest nations on Earth in the field of space exploration for many years. In this year, Esperanto -- presumably already gaining in popularity due to the need for close cooperation -- was declared to be the official language of participating nations. Within a decade, all children and many adults of these countries spoke Esperanto as a second language. Other nations would then fall in prominence within the United Nations while others would rise, and all of them would come to adopt Esperanto in order to participate on the world stage. By 2200, with the founding of the League of Old Earth Democracies, old nations and old borders were ceasing to have meaning. Children would begin to grow up speaking Esperanto as a first language, perhaps with an old "native" tongue as a second language, but increasingly, these old languages would become mere historical curiosities. For a modern example, look at the Welsh language, which would be continuing to die off if not for deliberate efforts to reverse its decline.
By Star Conquest's current year, Esperanto has been spoken for generations. It is the only language that the average individual grew up speaking and regularly hearing. There are two main exceptions to this: First, some communities left Old Earth before or during the period when Esperanto was becoming universal, and would have spoken their own language primarily, and even later communities might have made a concerted effort to return to their cultural roots once isolated from Old Earth. Second, there may be isolated and insular pockets on Old Earth that never had a larger presence on the world stage and saw no need to adopt the universal language, though these would grow more rare by the year and would only survive through deliberate intergenerational effort.
For the most part, though, any culture that originated from Old Earth within the past 150 years or has had unbroken contact with Old Earth and its colony worlds will exclusively speak Esperanto. This includes people of the EAOS, AEU, and Fringe, and even most spaceborne societies.
When it comes to character concepts, it is also true that many players want their characters to already be able to speak a second language. Of course, if all of them did, this would cease to feel like a rare exception and Esperanto would feel much less universal than it is meant to be. For this reason, we will generally only approve second languages for characters that have had their origins in highly insular or isolated communities -- something which should also be very rare.
There is also some occasional difficulty in roleplaying that we're all speaking Esperanto when, in fact, the game's common language among its players is English. Homophones, rhymes, and the like that work in English probably do not work in Esperanto. However, it is best to just gloss over this problem and pretend that they do. Just remember that when someone speaks to you in unintelligible technobabble, your sarcastic response should be "In Esperanto, please!"
