These are the numeric symbols returned for a locale and so far the decimal, group and percentSign are the only properties that can be overwritten:

numbers: {
        symbols: {
            decimal: ",",
            group: " ",
            list: ";",
            percentSign: "%",
            plusSign: "+",
            minusSign: "-",
            exponential: "E",
            superscriptingExponent: "×",
            perMille: "‰",
            infinity: "∞",
            nan: "NaN",
            timeSeparator: ":"
}

Please allow customizing the rest of the properties (minusSign, nan, timeSeparator, etc). There are certain projects, where those symbols need to be customized.