Why JFormatedTextField replaces decimal with comma

Hi to All! I have a POS Software which I have developed in Java, NetBeans IDE. I am deploying this software on a variety of Windows Computers / Laptops for 5 years. I have used JFormattedTextFields for double data type in the whole Software. And I have set Format of this field to two decimal places. For example if an user types 12.325 , then this field returns 12.32 , Taking another example if an user types 12 , then this field returns 12.00 This is the perfect functionality that I want and my Software is working fine on all the clients Desktops/Laptops.

But a weird problem occurred yesterday, when I gave demo to a new Italy Based Client. For example If I type/enter 12.35 in the JFormatedTextField it automatically replaces decimals with comma i-e it returns 12,35 Taking another example if You will type 5 , it is returning 5,00 automatically. And this is bug, I can't figure out why is this happening. First time I have faced this error. It is the same Software, same code and same Java Version. Kindly guide me about the problem

Note1- This error is occurring in case of JFormatedTextField only.
Note2- The Clients computer has Windows 10 Pro (But I think this is not the cause of error, because I have deployed my software on hundreds of clients on Window 7,8,10)

*Note3- My Client is Italian that's why he has set Italian Language on his Laptop From Windows Settings, that's why all System icons and Text appears in Italian on his laptop. But 3rd party software appear in same language in which that software intend to. My software's Language is English and all the labels and buttons appears in English in my Software and this is perfectly fine.
Only the problem is with JFormatedTextField as I mentioned above.
So I am thing about may be there is such a system setting which is cause of this change/Error on his Laptop.
Waiting for your guidance. Thanks in advance.