Automate the i18n_default_fonts testcase for Japanese.
    
    This is the automation of the optional testcase https://fedoraproject.org/wiki/QA:Testcase_i18n_default_fonts.
    The test implementation runs the same commands as the mentioned test
    case and checks the expected output. It is designed to run in the scope
    of postinstall tests when the language is set to "japanese".