Configuration Error with i18n.routing.redirectToDefaultLocale in Starlight

[yntpdotme]

What version of starlight are you using?

0.32.5

What version of astro are you using?

5.5.3

What package manager are you using?

bun, pnpm

What operating system are you using?

Mac

What browser are you using?

Chrome, Arc

Describe the Bug

When running dev script, I'm encountering a configuration error related to the i18n routing options.

❯ bun dev
> astro dev

[ERROR] [@astrojs/starlight] An error occurred while updating the config
The option `i18n.routing.redirectToDefaultLocale` is only useful when the `i18n.routing.prefixDefaultLocale` is set to `true`. Remove the option `i18n.routing.redirectToDefaultLocale`, or change its value to `true`.
 
 ELIFECYCLE  Command failed with exit code 1.

it's happening with a fresh empty project

[JeffryGonzalez]

Yep - getting the same thing. I'm using npm, node 22.14 and npm 11.2.0 on a mac.

[HiDeoo]

Thanks for the report 🙌

We are currently investigating the issue. A temporary workaround is to rollback the version of Astro to version 5.5.6.

[delucis]

Thanks for reporting the issue! Looks like an issue introduced in Astro 5.6.0 by #13482. We’re taking a look to see if the fix should be in Astro or Starlight.

In the meantime installing an Astro version lower than 5.6.0 should fix things, e.g.

npm install astro@5.5.6

Edit: You win this time @HiDeoo 😄

[delucis]

We’re going to fix this in Astro — thanks @ematipico for investigating!

[ematipico]

Can you please try the following preview release and report if fixes the bug?

#13552 (comment)

npm i https://pkg.pr.new/astro@13552