feat: migrate exampleSite to multilingual content directories

[htnabe]

Overview

This PR migrates the example site content to language-based directories and expands multilingual coverage to additional languages.
It also updates language switching behavior/tests and adds localized content/i18n resources for the new language set.

Changes

• Reorganized exampleSite/content into per-language directories via contentDir in exampleSite/config/_default/languages.yaml
• Added/updated multilingual pages (about, author, privacy) and post content for:
  • de, es, fr, hi, ko, zh-cn, zh-tw
• Added i18n files:
  • i18n/de.yaml, i18n/es.yaml, i18n/fr.yaml, i18n/hi.yaml, i18n/ko.yaml, i18n/zh-cn.yaml, i18n/zh-tw.yaml
• Added localized params.author.career entries by language in languages.yaml
• Updated docs for language-directory content organization:
  • docs/guidance/getting-started.en.md
  • docs/guidance/getting-started.ja.md
  • docs/develop/project-structure.md
• Updated header language-switcher spacing and language-switcher e2e tests for maintainability

Related Issues

N/A

Checklist

• Self-review done (following review.prompt.md)
• Hugo production build passes: cd exampleSite && hugo --gc --minify
• Docs updated if behavior changed
• No unrelated changes included

Notes for Reviewers

• Validation run locally:
  • npm test (pass)
  • npm run test:e2e (pass)
• Playwright/Hugo run shows deprecation warnings for Hugo language keys (languageCode/languageName and related template fields). These are not introduced as breaking changes in this PR but may need follow-up migration to locale/label.

[Copilot]

Pull request overview

This PR migrates the theme’s exampleSite content to per-language content directories (via contentDir) and expands multilingual coverage, including updated language-switcher UI spacing and E2E test expectations.

Changes:

• Reorganized exampleSite/content into language-based directories and updated exampleSite/config/_default/languages.yaml to use contentDir per language.
• Added localized content pages/posts and i18n resources for additional languages (de/es/fr/hi/ko/zh-cn/zh-tw).
• Updated the header language-switcher spacing and strengthened Playwright E2E assertions around language switcher behavior.

Findings

• Major
  • tests/e2e/navigation.spec.ts: The new toBaseLanguageCode() logic collapses region tags (e.g. zh-cn/zh-tw) and can miss real hreflang/lang mismatches between region variants. (comment ID: 001)
• Nit
  • exampleSite/content/fr/privacy.md: Missing expected French diacritics/accents in user-facing text. (comment ID: 002)
  • exampleSite/content/es/privacy.md: Missing expected Spanish diacritics/accents in user-facing text. (comment ID: 003)
  • exampleSite/config/_default/languages.yaml: French career string missing accent in “ingénieur”. (comment ID: 004)

Reviewed changes

Copilot reviewed 57 out of 71 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/e2e/navigation.spec.ts	Updates language-switcher E2E tests and adds zh-cn navigation coverage.
layouts/partials/header.html	Adds consistent horizontal spacing (px-1) for header nav items including the language dropdown.
i18n/de.yaml	Adds German UI translations for theme strings.
i18n/es.yaml	Adds Spanish UI translations for theme strings.
i18n/fr.yaml	Adds French UI translations for theme strings.
i18n/hi.yaml	Adds Hindi UI translations for theme strings.
i18n/ko.yaml	Adds Korean UI translations for theme strings.
i18n/zh-cn.yaml	Adds Simplified Chinese UI translations for theme strings.
i18n/zh-tw.yaml	Adds Traditional Chinese UI translations for theme strings.
exampleSite/config/_default/languages.yaml	Defines contentDir per language and localizes author career entries by language.
docs/guidance/getting-started.en.md	Documents language-directory content organization using contentDir.
docs/guidance/getting-started.ja.md	Documents language-directory content organization using contentDir.
docs/develop/project-structure.md	Updates project structure docs to reflect language-based content directories.
exampleSite/content/posts/tech/choosing-fonts-for-the-web.md	Removes the non-language-scoped version of the post (moved into language dirs).
exampleSite/content/en/about.md	Adds English About page under language directory.
exampleSite/content/en/author.md	Adds English Author page under language directory.
exampleSite/content/en/privacy.md	Adds English Privacy page under language directory.
exampleSite/content/en/posts/daily/protect-environment.md	Adds an English Daily post under language directory.
exampleSite/content/en/posts/math/matrix.md	Adds an English Math post under language directory.
exampleSite/content/en/posts/review/head-light.md	Adds an English Review post under language directory.
exampleSite/content/en/posts/tech/hello-world.md	Adds an English Tech post under language directory.
exampleSite/content/ja/about.md	Adds Japanese About page under language directory.
exampleSite/content/ja/author.md	Adds Japanese Author page under language directory.
exampleSite/content/ja/privacy.md	Adds Japanese Privacy page under language directory.
exampleSite/content/ja/posts/daily/protect-environment.md	Adds a Japanese Daily post under language directory.
exampleSite/content/ja/posts/math/matrix.md	Adds a Japanese Math post under language directory.
exampleSite/content/ja/posts/review/head-light.md	Adds a Japanese Review post under language directory.
exampleSite/content/ja/posts/tech/choosing-fonts-for-the-web.md	Adds a Japanese Tech post under language directory.
exampleSite/content/ja/posts/tech/hello-world.md	Adds a Japanese Tech post under language directory.
exampleSite/content/ko/about.md	Adds Korean About page under language directory.
exampleSite/content/ko/author.md	Adds Korean Author page under language directory.
exampleSite/content/ko/privacy.md	Adds Korean Privacy page under language directory.
exampleSite/content/ko/posts/daily/protect-environment.md	Adds a Korean Daily post under language directory.
exampleSite/content/ko/posts/tech/choosing-fonts-for-the-web.md	Adds a Korean Tech post under language directory.
exampleSite/content/ko/posts/tech/hello-world.md	Adds a Korean Tech post under language directory.
exampleSite/content/de/about.md	Adds German About page under language directory.
exampleSite/content/de/author.md	Adds German Author page under language directory.
exampleSite/content/de/privacy.md	Adds German Privacy page under language directory.
exampleSite/content/de/posts/daily/protect-environment.md	Adds a German Daily post under language directory.
exampleSite/content/de/posts/tech/choosing-fonts-for-the-web.md	Adds a German Tech post under language directory.
exampleSite/content/de/posts/tech/hello-world.md	Adds a German Tech post under language directory.
exampleSite/content/fr/about.md	Adds French About page under language directory.
exampleSite/content/fr/author.md	Adds French Author page under language directory.
exampleSite/content/fr/privacy.md	Adds French Privacy page under language directory.
exampleSite/content/fr/posts/daily/protect-environment.md	Adds a French Daily post under language directory.
exampleSite/content/fr/posts/tech/choosing-fonts-for-the-web.md	Adds a French Tech post under language directory.
exampleSite/content/fr/posts/tech/hello-world.md	Adds a French Tech post under language directory.
exampleSite/content/es/about.md	Adds Spanish About page under language directory.
exampleSite/content/es/author.md	Adds Spanish Author page under language directory.
exampleSite/content/es/privacy.md	Adds Spanish Privacy page under language directory.
exampleSite/content/es/posts/daily/protect-environment.md	Adds a Spanish Daily post under language directory.
exampleSite/content/es/posts/tech/choosing-fonts-for-the-web.md	Adds a Spanish Tech post under language directory.
exampleSite/content/es/posts/tech/hello-world.md	Adds a Spanish Tech post under language directory.
exampleSite/content/hi/about.md	Adds Hindi About page under language directory.
exampleSite/content/hi/author.md	Adds Hindi Author page under language directory.
exampleSite/content/hi/privacy.md	Adds Hindi Privacy page under language directory.
exampleSite/content/hi/posts/daily/protect-environment.md	Adds a Hindi Daily post under language directory.
exampleSite/content/hi/posts/tech/choosing-fonts-for-the-web.md	Adds a Hindi Tech post under language directory.
exampleSite/content/hi/posts/tech/hello-world.md	Adds a Hindi Tech post under language directory.
exampleSite/content/zh-cn/about.md	Adds Simplified Chinese About page under language directory.
exampleSite/content/zh-cn/author.md	Adds Simplified Chinese Author page under language directory.
exampleSite/content/zh-cn/privacy.md	Adds Simplified Chinese Privacy page under language directory.
exampleSite/content/zh-cn/posts/daily/protect-environment.md	Adds a Simplified Chinese Daily post under language directory.
exampleSite/content/zh-cn/posts/tech/choosing-fonts-for-the-web.md	Adds a Simplified Chinese Tech post under language directory.
exampleSite/content/zh-cn/posts/tech/hello-world.md	Adds a Simplified Chinese Tech post under language directory.
exampleSite/content/zh-tw/about.md	Adds Traditional Chinese About page under language directory.
exampleSite/content/zh-tw/author.md	Adds Traditional Chinese Author page under language directory.
exampleSite/content/zh-tw/privacy.md	Adds Traditional Chinese Privacy page under language directory.
exampleSite/content/zh-tw/posts/daily/protect-environment.md	Adds a Traditional Chinese Daily post under language directory.
exampleSite/content/zh-tw/posts/tech/choosing-fonts-for-the-web.md	Adds a Traditional Chinese Tech post under language directory.
exampleSite/content/zh-tw/posts/tech/hello-world.md	Adds a Traditional Chinese Tech post under language directory.