Thank you Rinke Hoekstra for your advice.
I will left the 18n functionalities out of the application.
I don't agree with you when you say
no numbers are to be entered, compared or interpreted by the user, so also no number formatting is needed, ...
It is written in the assignment:
Your user interface should be designed with the expectation of future functionality
enhancements, and it should establish a framework ...
and
Object-oriented design (30 points)
so I think that it is better to convert the
into business objects, i.e. in numbers when necessary.