> Is there any way to extend support?
No.
> or do you have any idea how to work around it?
Yes, lots. It completely depends on what you wish to achieve.
> Should I write custom properties panel to handle this behavior with shared parameters?
Yes, that is probably the best approach.
> I see everything in metric but Revit compute this in imperial.
Revit uses the display units in your current settings in the user interface. I assume that you have set your display units to metric. The internal Revit database units for length measurements are in imperial feet.
So, if you wish to read length measurements from the Revit database and convert them to your current display units, you need to implement code to do so.
> I search for similar solution but for string not for double/int (Code in this situation is kind of different language).
The Revit API does not offer any support for handling multiple user interface languages, so you will have to handle that yourself.