Fix language switch

[apriljunge]

• correct url in language switch
• redirect wrong urls
• add alternate meta tags

Wrong urls

The same content can be accessed by multiple urls. For example

URL	gui lang	content lang	should redirect
/aktionen/[slug-de]	de	de	–
/actions/[slug-de]	de	de	/aktionen/[slug-de]
/aktionen/[slug-en]	de	en	/en/actions/[slug-en]
/actions/[slug-en]	de	en	/en/actions/[slug-en]
/en/actions/[slug-en]	en	en	–
/en/actions/[slug-de]	de	en	/aktionen/[slug-de]

[apriljunge]

I created a first draft to fix the language switch.
@azinazadi @Haliax @Moyaccercchi Can you review the draft if you think that would be a good solution?

Regarding the implementation, I have a pretty good idea how to fix the gui / content lang mismatch. But I have two open issues. If you know how to do this, please give me a hint:

• How to create a redirect in actions/[..slug].js?
• Why /actions/[slug-de] works? I guess it's an issue with the router, but I have no idea.

[azinazadi]

what is the state with your changes? does it work for actions?

[apriljunge]

what is the state with your changes? does it work for actions?

Yes, it works just for actions/[slug] not for /actions/. But it is easy to apply this approach to all other pages. I requested review to get feedback for the general approach to use the state and check if you have further ideas to my questions above.

What currently works:
Go to a specific action (e.g. /aktionen/graz-2026-02-22-get-together), click on en, then the page should change to /en/actions/graz-2026-02-22-get-together-en (the english version)

[Moyaccercchi]

We think we don't really understand your two questions / open issues ^^'
Could you describe a bit more what your problem with the redirects or the working page is?

Regarding this pull request:
If we understand this correctly, we call getLocalizedSlug asychronously on each request for each locale, but will only need it for the not-currently-selected locale... we would prefer a method where we only get the one we need, and ideally without any async requests, as we think for over 1000 views the language switch is only clicked once, so no need to load this all the time but instead just in the moment of the click do some custom logic?