[TheDong]

Having different registers, the "everyday language", and the "more formal, fancy sounding register", is far from unique to English, and I'd dare-say the majority of broadly used languages have some form of this.

In fact, English has it less than a lot of languages. In Japanese, you not only use different words when in a more formal register, you also conjugate verbs differently and use different honorific suffixes to refer to people. https://en.wikipedia.org/wiki/Honorific_speech_in_Japanese

I guess people who speak japanese can speak 4 languages (casual speech, normal polite desu/masu speech, humble speech, and keigo). They all have different word-choices and conjugations, and there's also similarly a dual-origin story of "some words came from ancient chinese, some from ancient japanese".