Multilang permalinks for Writer field

[distantnative]

Description

It looks to me like PhpUnit again ignores a test due to the method name, ::url does have unit tests.

Summary of changes

• ::permalink() now returns a localized permalink in a multilang setup
• Link dialog inserts localized permalinks when a current language is given

Reasoning

This should resolve #5551.
When language.detect setting is disabled, Kirby has no way to automatically figure out to which language to route a normal permalink. This is why the permalinks need to include the language code themselves, representing a permanent link to that page in this specific language. #6312 added the routing support for this. But this PR adds that those language-based permalinks are exposed in the right places:

• when put out via $page->permalink()
• when inserting a permalink in the writer field HTML

Additional context

I hope I have covered all cases to now convert not just normal permalinks but language-based permalinks back and forth with UUIDs and normal IDs in the Panel code.

@afbora It would be super valuable to get your expert testing skills thrown at this to be sure.

Changelog

Fixes

• Multilang: Writer field now inserts the correct permalink for the current content language
• Multilang: $page->permalink() returns a language-based permalink for the current content language

Ready?

• In-code documentation (wherever needed)
• Unit tests for fixed bug/feature
• Tests and CI checks all pass

For review team

• Add lab and/or sandbox examples (wherever helpful)
• Add changes & docs to release notes draft in Notion

[afbora]

Do you think we need language prefix for file permalinks? Is there any difference both /@/file/tWNX7ZrzJUvS9Vad and /en/@/file/tWNX7ZrzJUvS9Vad? AFAIK files are singular objects. But page contents are different according to access uri.

[distantnative]

@afbora Valid point. I'll check what's the best way to do just pages.