Port to i18next v4 format

Now that we have switched to i18next-parser we can also switch the json format to the newer version.

https://www.i18next.com/misc/json-format#i18next-json-v4

Todo:

• switch i18next-parser to v4
• switch the i18next init to v4
• port all apps, foreach:
  • update toolkit
  • switch i18next-parser to v4

v4 requires https://developer.mozilla.org/en-US/docs/web/javascript/reference/global_objects/intl/pluralrules

Which means we would drop support for Safari<13. If we do this then we need to add a check for (typeof Intl === 'undefined' || !Intl.PluralRules) to the browser check script.