The They/Them Pronoun
I use the they/them pronoun, to reflect my identity as a non-binary person. In the English language, they/them functions as a gender neutral pronoun, used when we don't know the gender of the person to whom we are referring. For example, imagine that you come across a lost piece of luggage. You might comment, "Someone left their bag here" or "Someone's bag has been left behind. We should return it to them." Because you do not know the bag's owner, you do not use gendered language in your speech. This same linguistic function is applied to people requesting the they/them pronoun to reflect a trans gender identity.
There are a number of other languages that have modes of gender neutral speech, as well as some that do not. For those that do not have a natural gender neutral pronoun, new forms of address are being formed by those that need them, and language is evolving. For further information on gender neutral forms of address, please do not hesitate to get in touch with me.