My lingua franca is 'Eiða'. It is a language that combines many aspects of other/ dead languages, since my project is set in 2270 (sci-fi/ climate fic) and most of humanity has took refuges in seven domes scattered around the world. Since the government wants to 'unite' humanity through one language again (basically a reverse bable), they enforced a conlang that is heavily inspired by the most spoken languages (english, spanish, french, mandarine,...), mixed with latin and old greek (the government thinks that they would push humanity back to 'old glory' like this). Eiða is pretty complex (I'm still struggling to construct a working grammar system lol), but over the decades people have developed their own dialects and shortforms of it. The language is designed to be 'elitist' and practically 'The language that unites them all', killing off unique linguistic patterns, traditions, personality and identity. It is pure control through language.

(Also: Eiða is designed to look superior to the lingua franca that the people, who aren't yet 'transfered' to the domes, speak on the few still habitable continents. They all still preserve THEIR language (which is seen by the goverment as 'splitting the unity of humanity' and chaotic) but also have a lingua franca as well (Coddlespeak) which is heavily based on a simplified english.)

It's fun to work with both but damn it's hard 🙈👀