feat(i18n): document new i18n logic

[ematipico]

Description (required)

This PR documents i18n.routing.fallbackType, a new feature that will change how the fallback works.

For Astro version: 4.15.0. See astro PR #11677

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Warnings reference

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🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[sarah11918]

@ematipico Take a look at what I've done and see what you think!

The existing Fallback content needed some revising anyway, because it described the existing behaviour of redirects everywhere.

Since this isn't a reference page, and we have full config reference items we can link to for fallback and fallbackType, this page can simply tell the story of what a fallback strategy looks like.

(Note, I will actually want to revisit the rest of this page in the same way at some point, but for now, let's just get the fallback in place!)

Let me know what you think of this, and whether seeing the big picture like this makes you want to e.g. move the option from i18n.routing and instead maybe rethink adding to fallback itself? When you look at what it takes to configure this, and how it is explained, you might think of a better way config could look to achieve a more complete fallback outcome. (setting in two places like this might seem a little clunky)

But, see what you think and let me know!

[ematipico]

Thank you @sarah11918 , I approve your new edits!

[sarah11918]

Noting that the link check should pass once the new config reference docs have been pulled in!

[sarah11918]

I think we're in a good place here! 🥳

[yanthomasdev]

LGTM!

[sarah11918]

!coauthor

[github-actions]

Co-authored-by: Houston (Bot) <[email protected]>
Co-authored-by: Sarah Rainsberger <[email protected]>
Co-authored-by: Yan <[email protected]>