Simple Convert.ToDouble will cause wrong input string Error [duplicate]

I want to parse a string like "3.5" to a double. However,

double.Parse("3.5") 

yields 35 and

double.Parse("3.5", System.Globalization.NumberStyles.AllowDecimalPoint) 

throws a FormatException.

Now my computer's locale is set to German, wherein a comma is used as decimal separator. It might have to do something with that and double.Parse() expecting "3,5" as input, but I'm not sure.

How can I parse a string containing a decimal number that may or may not be formatted as specified in my current locale?

double.Parse("3.5", CultureInfo.InvariantCulture)

I usualy use a multi-culture function to parse user input, mostly because if someone is used to the numpad and is using a culture that use a comma as the decimal separator, that person will use the point of the numpad instead of a comma.

public static double GetDouble(string value, double defaultValue)
{
    double result;

    //Try parsing in the current culture
    if (!double.TryParse(value, System.Globalization.NumberStyles.Any, CultureInfo.CurrentCulture, out result) &&
        //Then try in US english
        !double.TryParse(value, System.Globalization.NumberStyles.Any, CultureInfo.GetCultureInfo("en-US"), out result) &&
        //Then in neutral language
        !double.TryParse(value, System.Globalization.NumberStyles.Any, CultureInfo.InvariantCulture, out result))
    {
        result = defaultValue;
    }

    return result;
}

Beware though, @nikie comments are true. To my defense, I use this function in a controlled environment where I know that the culture can either be en-US, en-CA or fr-CA. I use this function because in French, we use the comma as a decimal separator, but anybody who ever worked in finance will always use the decimal separator on the numpad, but this is a point, not a comma. So even in the fr-CA culture, I need to parse number that will have a point as the decimal separator.