feat: Modernize internationalization system with Jekyll Polyglot

BREAKING CHANGE: Complete overhaul of multilingual architecture

## Major Changes

### Architecture Modernization
- **Eliminated 80% code duplication**: Replaced 65+ duplicate HTML files with 13 centralized templates
- **Implemented Jekyll Polyglot**: Modern plugin-based internationalization system
- **Automatic language generation**: No more manual language directory management
- **Data-driven translations**: Centralized translation files in _data/{lang}.yml

### File Structure Changes
- **REMOVED**: All duplicate language directories (app/en/, app/fr/, app/es/, app/cs/)
- **REMOVED**: Unused _locales/ directory with generic Rails i18n files
- **ADDED**: Centralized page templates in app/ root directory
- **UPDATED**: Translation system to use site.data[locale] with Jekyll Polyglot

### Language Support
- **Maintained**: Full support for English, French, Spanish, Czech
- **Improved**: URLs now properly route (/fr/, /es/, /cs/)
- **Enhanced**: Language switcher updated for Jekyll Polyglot compatibility
- **Verified**: All translations working correctly across all languages

### Performance Optimizations
- **Build performance**: Added incremental builds, SASS compression
- **Liquid optimization**: Strict filters and error handling
- **Parallel localization**: Enabled for faster multi-language builds
- **Better exclusions**: Improved build exclusions for faster processing

### Testing & Quality Assurance
- **NEW**: Comprehensive test suite (test-multilingual.sh)
- **NEW**: GitHub Actions workflow for automated multilingual testing
- **VERIFIED**: All 6 test categories passing:
  - Jekyll build verification
  - Language directory structure validation
  - Translation content verification
  - Feed generation verification
  - Asset exclusion verification
  - Polyglot configuration validation

### Developer Experience
- **NEW**: Complete documentation (INTERNATIONALIZATION.md)
- **NEW**: Quick reference guide (QUICK-REFERENCE.md)
- **UPDATED**: README with modern system documentation
- **ADDED**: Performance configuration (_config-performance.yml)

### Configuration Updates
- **Jekyll Polyglot**: Added plugin configuration to _config.yml
- **Locale detection**: Updated get_locale.html to use site.active_lang
- **Language switcher**: Modernized header.html navigation
- **Dependencies**: Updated Gemfile with jekyll-polyglot plugin

## Benefits Achieved

### Maintainability
- **Single source of truth**: One template per page type
- **Simplified updates**: Changes apply to all languages automatically
- **Reduced maintenance**: No more syncing across language directories
- **Clear separation**: Templates vs translations cleanly separated

### Performance
- **Faster builds**: Parallel localization and incremental builds
- **Smaller repo**: Eliminated redundant files
- **Better caching**: Improved Jekyll cache configuration
- **Optimized assets**: Compressed SASS and optimized exclusions

### Quality
- **Automated testing**: Prevents regression in multilingual functionality
- **Documentation**: Comprehensive guides for future maintainers
- **CI/CD integration**: Automated testing in GitHub Actions
- **Error prevention**: Strict Liquid templates and validation

## Migration Impact
- **No content loss**: All existing translations preserved
- **URL compatibility**: All language URLs continue to work
- **Feature parity**: All functionality maintained
- **Improved reliability**: More robust language switching and routing

## Technical Details
- **Plugin**: jekyll-polyglot v1.11.0
- **Languages**: en (default), fr, es, cs
- **Templates**: 13 centralized HTML files
- **Translations**: 4 YAML data files
- **Testing**: 6-category comprehensive test suite
- **Documentation**: 2 detailed guides + updated README

This modernization provides a solid foundation for future development
and significantly improves the maintainability of the multilingual system.

Author: Dale Kunce

.github/workflows/test-multilingual.yml

@@ -0,0 +1,50 @@
+name: Jekyll Polyglot Multilingual Tests
+
+on:
+  push:
+    branches: [ main, modernize-2025 ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test-multilingual:
+    runs-on: ubuntu-latest
+    
+    steps:
+    - uses: actions/checkout@v3
+    
+    - name: Setup Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: '3.0'
+        bundler-cache: true
+    
+    - name: Setup Node.js
+      uses: actions/setup-node@v3
+      with:
+        node-version: '18'
+        cache: 'npm'
+    
+    - name: Install dependencies
+      run: |
+        bundle install
+        npm install
+    
+    - name: Run Jekyll build
+      run: bundle exec jekyll build
+    
+    - name: Run multilingual tests
+      run: ./test-multilingual.sh
+    
+    - name: Check for broken links (sample)
+      run: |
+        # Basic link verification for main pages
+        for lang in "" "fr/" "es/" "cs/"; do
+          echo "Checking ${lang:-en} pages..."
+          if [ -f "_site/${lang}about/index.html" ]; then
+            echo "✅ ${lang:-en}about page exists"
+          else
+            echo "❌ ${lang:-en}about page missing"
+            exit 1
+          fi
+        done

Gemfile

@@ -9,6 +9,7 @@ gem "jekyll", "~> 4.3.4"
 # Jekyll plugins
 gem "jekyll-feed", "~> 0.17"
 gem "jekyll-sitemap", "~> 1.4"
+gem "jekyll-polyglot", "~> 1.8"
 
 # Additional gems for security and performance
 gem "webrick", "~> 1.8" # Required for Ruby 3.0+

Gemfile.lock

@@ -46,6 +46,8 @@ GEM
       webrick (~> 1.7)
     jekyll-feed (0.17.0)
       jekyll (>= 3.7, < 5.0)
+    jekyll-polyglot (1.11.0)
+      jekyll (>= 4.0, >= 3.0)
     jekyll-sass-converter (3.1.0)
       sass-embedded (~> 1.75)
     jekyll-sitemap (1.4.0)
@@ -96,6 +98,7 @@ DEPENDENCIES
   csv (~> 3.3)
   jekyll (~> 4.3.4)
   jekyll-feed (~> 0.17)
+  jekyll-polyglot (~> 1.8)
   jekyll-sitemap (~> 1.4)
   logger (~> 1.6)
   ostruct (~> 0.6)

INTERNATIONALIZATION.md

@@ -0,0 +1,264 @@
+# Missing Maps Jekyll Polyglot Internationalization System
+
+## Overview
+
+This document describes the modernized internationalization (i18n) system for the Missing Maps website, which uses Jekyll Polyglot to support multiple languages efficiently.
+
+## Architecture
+
+### Before (Legacy System)
+- **65+ duplicate HTML files** across 4 language directories (`/en/`, `/fr/`, `/es/`, `/cs/`)
+- Manual URL parsing for locale detection
+- Maintenance nightmare with code duplication
+
+### After (Jekyll Polyglot System)
+- **13 centralized templates** in `/app/` root directory
+- **Automatic language generation** by Jekyll Polyglot plugin
+- **Single source of truth** for page structure
+- **Data-driven translations** via `_data/{lang}.yml` files
+
+## Languages Supported
+
+| Language | Code | URL Pattern | Data File |
+|----------|------|-------------|-----------|
+| English  | `en` | `/` (root)  | `_data/en.yml` |
+| French   | `fr` | `/fr/`      | `_data/fr.yml` |
+| Spanish  | `es` | `/es/`      | `_data/es.yml` |
+| Czech    | `cs` | `/cs/`      | `_data/cs.yml` |
+
+## Key Components
+
+### 1. Configuration (_config.yml)
+
+```yaml
+# Jekyll Polyglot Configuration
+languages: ["en", "fr", "cs", "es"]
+default_lang: "en"
+exclude_from_localization: ["assets", "scripts", "styles", "images", "favicon.ico", "robots.txt", "humans.txt", "CNAME", "Process-1.svg"]
+parallel_localization: true
+
+plugins:
+  - jekyll-polyglot
+```
+
+### 2. Page Templates
+
+All page templates are located in `/app/` root:
+- `index.html` - Homepage
+- `about.html` - About page  
+- `advanced.html` - Advanced tutorials
+- `beginner.html` - Beginner tutorials
+- `blog.html` - Blog listing
+- `categories.html` - Category view
+- `events.html` - Events page
+- `field.html` - Field mapping
+- `host.html` - Host page
+- `mapswipe.html` - MapSwipe
+- `statistics.html` - Statistics
+- `tags.html` - Tag view
+- `validate.html` - Validation
+
+### 3. Locale Detection
+
+The `_includes/get_locale.html` include sets the locale variable:
+
+```liquid
+{% assign locale = site.active_lang %}
+```
+
+### 4. Translation Data
+
+Translations are stored in YAML files under `_data/`:
+
+**Structure Example (`_data/en.yml`):**
+```yaml
+about:
+  title: "About"
+  who_we_are:
+    title: "Who we are"
+    text1: "Missing Maps is a project..."
+  objectives:
+    title: "Objectives"
+    text1: "To map areas where people live..."
+```
+
+**Usage in Templates:**
+```liquid
+<h1>{{site.data[locale].about.title}}</h1>
+<p>{{site.data[locale].about.who_we_are.text1}}</p>
+```
+
+### 5. Language Switcher
+
+Updated to work with Jekyll Polyglot in `_includes/header.html`:
+
+```liquid
+{% for lang in site.languages %}
+  {% if lang == site.default_lang %}
+    <a href="{{site.baseurl}}{{page.url | remove_first: '/' | remove_first: locale | prepend: '/'}}">
+      <div class="nav-item item-centered">{{lang}}</div>
+    </a>
+  {% else %}
+    <a href="{{site.baseurl}}/{{lang}}{{page.url | remove_first: '/' | remove_first: locale | prepend: '/'}}">
+      <div class="nav-item item-centered">{{lang}}</div>
+    </a>
+  {% endif %}
+{% endfor %}
+```
+
+## Build Process
+
+### Development
+```bash
+npm run serve
+# Builds site with Jekyll Polyglot and starts development server
+```
+
+### Production Build
+```bash
+npm run build
+# Optimized build with SASS compression and asset optimization
+```
+
+### Testing
+```bash
+./test-multilingual.sh
+# Runs comprehensive multilingual functionality tests
+```
+
+## Generated Output
+
+Jekyll Polyglot automatically generates:
+
+```
+_site/
+├── index.html              # English homepage
+├── about/                  # English about page
+├── assets/                 # Shared assets
+├── fr/
+│   ├── index.html         # French homepage  
+│   ├── about/             # French about page
+│   └── feed.xml           # French RSS feed
+├── es/
+│   ├── index.html         # Spanish homepage
+│   ├── about/             # Spanish about page  
+│   └── feed.xml           # Spanish RSS feed
+└── cs/
+    ├── index.html         # Czech homepage
+    ├── about/             # Czech about page
+    └── feed.xml           # Czech RSS feed
+```
+
+## Performance Optimizations
+
+### Jekyll Configuration
+- **Incremental builds**: `incremental: true`
+- **SASS compression**: `style: compressed`
+- **Parallel localization**: `parallel_localization: true`
+- **Liquid optimization**: `strict_filters: true`
+
+### Build Exclusions
+- `node_modules/`
+- `package.json`
+- `gulpfile.cjs`
+- `.sass-cache/`
+- `.jekyll-cache/`
+
+## Adding New Languages
+
+1. **Add language code** to `_config.yml`:
+   ```yaml
+   languages: ["en", "fr", "cs", "es", "de"]  # Added German
+   ```
+
+2. **Create translation file** `_data/de.yml`:
+   ```yaml
+   about:
+     title: "Über uns"
+     # ... translations
+   ```
+
+3. **Rebuild site**: Jekyll Polyglot will automatically generate `/de/` routes
+
+## Adding New Pages
+
+1. **Create template** in `/app/`:
+   ```html
+   ---
+   layout: default
+   permalink: /newpage/
+   id: newpage
+   ---
+   {% include get_locale.html %}
+   {% include header.html %}
+   <h1>{{site.data[locale].newpage.title}}</h1>
+   ```
+
+2. **Add translations** to all `_data/{lang}.yml` files:
+   ```yaml
+   newpage:
+     title: "New Page Title"
+   ```
+
+## Troubleshooting
+
+### Common Issues
+
+**Language pages not generating:**
+- Check `languages` array in `_config.yml`
+- Ensure page templates are in `/app/` root, not subdirectories
+- Verify `jekyll-polyglot` plugin is installed and listed
+
+**Translations not showing:**
+- Check `locale` variable is set via `{% include get_locale.html %}`
+- Verify translation keys exist in `_data/{lang}.yml`
+- Ensure correct Liquid syntax: `{{site.data[locale].key}}`
+
+**Build errors:**
+- Run `bundle exec jekyll build --trace` for detailed error info
+- Check for YAML syntax errors in `_data/` files
+- Verify all required translations exist for each language
+
+### Debugging Commands
+
+```bash
+# Full build with error details
+bundle exec jekyll build --trace
+
+# Test translations
+./test-multilingual.sh
+
+# Check generated structure
+ls -la _site/*/
+
+# Verify specific language content
+grep "feature-header" _site/fr/about/index.html
+```
+
+## Migration from Legacy System
+
+The migration eliminated:
+- **52 duplicate English files** (moved to templates)
+- **4 language directories** (auto-generated now)
+- **Old locale detection logic** (replaced with Polyglot)
+- **Manual URL construction** (handled by plugin)
+
+### Benefits Achieved
+- 🚀 **80% reduction in code duplication**
+- 🔧 **Simplified maintenance** (single templates)
+- 🌐 **Consistent translation system**
+- ⚡ **Improved build performance**
+- 🧪 **Automated testing coverage**
+
+## Support & Maintenance
+
+For issues or questions:
+1. Check this documentation
+2. Run test suite: `./test-multilingual.sh`
+3. Review Jekyll Polyglot docs: https://github.com/untra/polyglot
+4. Check build logs for specific errors
+
+---
+
+*Last updated: October 2025*
+*System version: Jekyll Polyglot v1.11.0*