Reset your own CultureInfoby changing the default:
var cInfo = CultureInfo.CreateSpecificCulture("en-us");
cInfo.NumberFormat.NumberDecimalSeparator = ",";
cInfo.NumberFormat.CurrencyGroupSeparator = ",";
cInfo.NumberFormat.PercentDecimalSeparator = ",";
Thread.CurrentThread.CurrentCulture = cInfo;
Thread.CurrentThread.CurrentUICulture = cInfo;
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