I have made a testing version which should address this.
It has a new option on Settings -> Advanced Settings tab called “Apply Separators Settings To Customer Input”. Check it, save settings and your customers will be able to use your currently configured decimal separator (comma in your case) to enter values.
You can download it here https://s-plugins.com/testing/stripe-payments_1.8.9t1.zip . Just delete the one currently installed and install this one. Your settings and products would stay untouched. This testing version can also be updated to stable once it’s released without the need to delete it and re-install again.
Let me know if there it works like expected.