With same-sex relationships a possibility since the first game in the series back in 2000, The Sims 4.
With this update, a brand new or existing Sim can use the Create a Sim menu to choose They/Them from the Change Pronouns dropdown, or go into Custom Pronouns and set separate options for subjective, objective, reflexive, possessive dependent, and possessive independent pronouns. It seems like a pretty robust set of possibilities, and was designed with consultation from GLAAD and the It Gets Better Project, a nonprofit organization that The Sims partnered with in 2019.
Credit for getting the ball rolling should go to Twitch streamer and It Gets Better ambassador Momo Misfortune, who began tweeting daily at both EA and The Sims to request pronoun options early last year. They also started a petition on Change.org that accumulated 22,856 signatures.
In a blog post about the update, producer John Faciane, AKA SimGuruDuck, discussed the work that had gone into researching and adding this feature. "We went through a couple of different explorations," Faciane wrote, "but ultimately where we landed was to create a system that allows for pronouns to be defined by the player and have those then be used in multiple different text strings. This was achieved through creation of new tokens, or bits of text that are reused, that custom input from players."
Custom pronouns are currently only available for Sims in the English version of The Sims 4. Faciane noted it's going to take time to roll out given that The Sims 4 has been translated into 18 different languages: "With this amount of languages there is a lot of complexity around how different languages and cultures use pronouns, so we'll need additional time to research how to properly integrate grammar rules into other languages that the game is available in."
