Other way around, actually: he started out making constructed languages for fun, realized that doing that properly required inventing the cultural and historical context in which it developed, and then, later, started writing fiction set in that world.
Technically it’s an alphabet, not a language (excluding the keys with actual words on them and not just letters). The letters are called Tengwar and in the lore they’re Elvish letters, but you can use them to write in other languages like English. Even in universe they’re used for other languages like on the inscription of the One Ring, which is in Black Speech.
It's accurate in that it matches the popular LOTR fonts, but you can't just type normally and have the correct words appear without first running it through a program.
Edit:
Fun fact: currently you need to use special fonts to type these. But in the near future, they will be probably be officially added to Unicode, in the U+16080 to U+160FF range. This is because Computer Scientists are all nerds.