Add Japanese language support & translate some docs into Japanese

[morinokami]

What kind of changes does this PR include?

• Changes or translations of Starlight docs site content
• Changes to Starlight code

Description

• Add Japanese language support.
• Translate some pages of the docs into Japanese.

[changeset-bot]

🦋 Changeset detected

Latest commit: 9a1cdfd

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@astrojs/starlight	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

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[morinokami]

Hi, @delucis. While this PR includes changes to the Starlight code, the majority of the changes are translations. Should I add a changeset in this case?

[delucis]

Thanks for this @morinokami!

Yes, we should add a patch changeset so that the next release notes say that Japanese support was added 🥳

You can add one by running pnpm changeset add in the repo or clicking the “add a changeset” link in the bot message above. Let me know if you have any questions.

We should also update this line in the i18n docs to mention Japanese support:

starlight/docs/src/content/docs/guides/i18n.md

Line 113 in de24b54

We aim to ship these labels in as many languages as possible but currently only have support for English, German, and Spanish.

[delucis]

Thanks again @morinokami. I made those changes so I can release this tonight — will also make one more tweak.

[morinokami]

@delucis Ah, it was the middle of the night in Japan, so I had to stop working on it😅 Thank you for taking over and completing the rest!