allow multiple values for some properties if language differs

[haansn08]

This PR allows some properties (namely NAME, SUMMARY, DESCRIPTION and LOCATION) to be localized.

Here is an example item from a shopping list localized in German and Japanese which the current validator recognizes as invalid since the SUMMARY property is found twice. The logic in this PR counts the languages separately.

BEGIN:VTODO
DTSTAMP:20230916T091036Z
STATUS:COMPLETED
SUMMARY;LANGUAGE=de:Milch
SUMMARY;LANGUAGE=ja:牛乳
END:VTODO

[haansn08]

I no longer think this is the correct way to implement this. Instead this functionality should be implemented with the ALTID parameter as described in https://datatracker.ietf.org/doc/html/rfc6350#section-5.4