Large numbers by default are grouped together, often making it less easy to read without separators. The Global Commas Delimiter Scriptlet separates large numbers with commas, thus: 1848954 becomes 1,848,954. This applies to windows wherever gold is displayed (on the status or in shops).
You don’t need to alter anything in the Window_Gold, Window_ShopBuy or Window_ShopSell windows. This scriptlet does it automatically.
A new method, to_comma to Window_Base so you can use it to delimiter any large number with commas. Just add .to_comma(n), where n is the number to convert.