English has Rules, Just Like Japanese!

[Mhaeric]

Singular they has been a thing in modern English due to the fact that the language doesn't have a third person singular pronoun that is both gender neutral and of indefinite number that can be used to refer back to another s. The plural pronouns they, them, their and themselves are commonly used by someone using English when they have need of such a pronoun. For example, the previous sentence made use of it to refer to the pronoun "someone."

Fun fact:

Just this week, Merriam-Webster officially added the word "they" to their dictionary as a singular pronoun for someone whose gender identity is non-binary.

https://www.merriam-webster.com/dictionary/they