Translate qualifierMessage

[dsuket]

Description

• I implemented internationalization for QualifierMessage.
• I moved the output of QualifierMessage from the plugin to the theme side.
  • Along with this change, I removed unnecessary methods from the plugin.
• Added the ja resource file.
• Fix snapshot

Motivation and Context

The QualifierMessage was not internationalized, so I fixed it.

How Has This Been Tested?

• Updated and executed the tests.
• I ran it locally and checked.

Screenshots (if appropriate)

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes if appropriate.
• All new and existing tests passed.

[github-actions]

Visit the preview URL for this PR (updated for commit b6afb5e):

https://docusaurus-openapi-36b86--pr1249-5y63xwne.web.app

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[sserrata]

Thanks @dsuket! The i18n approach looks solid — moving translatable strings from the plugin to the theme is the right move.

Questions before merging:

• Demo config change — Adding i18n: { locales: ["en", "ja"] } enables multi-locale builds for the demo site. Is this intentional going forward, or was it just for testing? If just for testing, please remove it. If intentional, please document why in the PR description.
• String coverage — Are all hardcoded strings in getQualifierMessage now translatable? (e.g., "non-empty", ">= X characters", "Value must match regular expression")
• Plugin export — Is getQualifierMessage still exported from the plugin for backward compatibility, or is it being removed? Should we flag it for future cleanup?