For Arabic specifically, different users want text to render differently, so you'd want to do it on the client if you can.

(Some countries use Roman numerals and some use Arabic numerals for numbers. And by Arabic numerals I don't mean 1-9.)

All Arabic-speaking countries use Arabic numerals. Some use Western Arabic numerals (123) and some use Eastern Arabic numerals (١٢٣).

Roman numerals are I, V, X, etc.