Decimal Seperator different in VBA and Excel

Question

I use "." as decimal separator in Excel. When I check the separator in VBA with Application.DecimalSeparator, it returns correctly (.). Nevertheless, if I pass a variable to my VBA-function, VBA encodes the double always like 0,11 instead of 0.11 and even if I write Application.DecimalSeparator = "." and Application.UseSystemSeperators = False in my function, it doesn't change.

Why is VBA using a different separator as Excel and how can one solve this problem?