Implement internationalization support for English and Japanese

[Copilot]

Adds bilingual support (English/Japanese) to enable international usage.

Changes

• Custom i18n implementation - Lightweight key-path based translation system without external dependencies
• Language switcher UI - Inline buttons with active state indication
• Translation structure - Embedded translations in js/i18n.js with separate JSON files in locales/ for reference

Implementation

// Simple translation lookup via dot notation
i18n.t('features.item1.title')  // "Multilingual Support" or "多言語対応"

// Language switching updates all [data-i18n] elements
changeLanguage('ja')  // Switches to Japanese

Translation keys are referenced via data-i18n attributes in HTML:

<h1 data-i18n="title"></h1>
<p data-i18n="description"></p>

Screenshots

English:

Japanese:

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• cdn.jsdelivr.net
  • Triggering command: /usr/bin/curl curl -o js/i18next.min.js REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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