When the OS is set to a country's locale that uses a number format different from en_US(1.1223), for example de_DE (1,1223), then the program tries to use this for all numerical operations.  For example:

This will not work:
    print (1.13241 + 4.11234);

But instead this will:
    print ("1,13241" + "4,11234");

Without the quotes would cause a parse error.

This is obviously unacceptable as no program can be ported.