Do not set any pattern (make sure to remove it). Instead, in the TextFieldExpression field use
new java.text.DecimalFormat("#,##0.00", new java.text.DecimalFormatSymbols(java.util.Locale.GERMANY)).format($P{parameter1}).
(This is a string. If your textfield expression class is double, you can parse the result.) This will format the number as in German locale for all languages.