system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do all the countries in the world use the same number system, but different languages?
gpt
Do you mean the written numbers? Or do you mean the base of the number system?

The Arabic numerals were created in India and then everyone else borrowed them because they worked really well or they didn't already have a number system of their own. They replaced Roman numerals because Roman numerals are clunky. But not everyone uses Arabic numerals. In Arabic, they actually have a different written number system. There's probably some other lesser known systems as well.

If you're talking about the structure of the number system, such as the base, that varies a lot. Some languages use base 12 or base 20. French uses a vigesimal system between 70 and 99. Some languages don't have numbers greater than 2 or 3.