[Enhancement] Add localization/translation of internal labels

[RasmusKjeldgaard]

• I have written a good issue

Describe the enhancement

Some labels and text content inside components should have proper translations according to our supported locale.
For instance, the previous/next month buttons of kirby-calendar or the close button of the modal are hidden from consumers of the component, and we should add a sensible translation.

Describe the solution you'd like

Should be researched! Shoelace has some considerations that are worth exploring: https://shoelace.style/getting-started/localization

Have you considered any alternatives?

If we choose to bake in the translations, consumers will not have to import translation assets into their own projects, and configure kirby. It will just work out of the box.
But a trade-off is that new or custom translations cannot be added easily by projects. Consider adding an option to override the default translations per locale.

Are there any additional context?

This is an initial list of identified translations:

• Calendar
  • Previous month
  • Next month
  • Year navigator
• Page back button
• Slides
  • Previous slide
  • Next slide
• Modal
  • Close
  • Supplementary action

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