Use Locale.ENGLISH when parsing dates in Converter.DATE

[rootvector2]

Converter.DATE parses with a default-locale SimpleDateFormat, but its documented input (the output of Date.toString()) always uses English month and day names, so a Date-typed option throws ParseException under any non-English default locale; pinning Locale.ENGLISH keeps the documented round-trip stable, which is also why testCreateDate already needed a @DefaultLocale pin.

[garydgregory]

Hello @rootvector2
How do you avoid breaking existing apps? Try to parse it twice? Rebase on git master and see the new test:
org.apache.commons.cli.ConverterTests.testDateLocaleDe()

[rootvector2]

Rebased on master. You're right that pinning Locale.ENGLISH outright would break testDateLocaleDe and any app passing a default-locale string, so I went with the parse-twice route: Converter.DATE now parses with the default locale first and only falls back to Locale.ENGLISH when that throws. Anything that parses today hits the exact same first parse, so existing behavior is unchanged; the fallback only covers the Date.toString() output, which is always English regardless of locale. Added testDateLocaleDeEnglishInput to lock that path under a de default. Both it and your testDateLocaleDe pass.