Large balances should be displayed with some kind of a thousands separator. This is frequently a comma, as in "1,000,000"
However, some countries use the comma as a decimal separator. A simple space, as in "1 000 000" is more universal. Regional customization would be best, but that can wait.
This diffs implements a space as the default thousands separator and adds a unit test to confirm separator is not added to numbers after the decimal place.