Rewrite ~120 validation error messages across 17 English lesson modules
and their localized variants (ar, de, es, pl, uk) to use concept questions,
property hints, and directional nudges instead of revealing the exact
CSS property-value answers.
Priority modules (flexbox, box-model, colors, positioning) fully rewritten.
All remaining CSS modules updated. Only message strings changed — no
validation logic modifications.
- Add German HTML entry point (index.de.html)
- Add German app.js with translated UI strings (app.de.js)
- Add German lesson config (lessons.de.js)
- Add German translations of all 6 lesson modules:
- HTML Elements: Block vs Inline
- HTML Forms: Basic Inputs
- HTML Forms: Validation
- CSS: Basic Selectors
- CSS: Advanced Selectors
- Tailwind: Basics
All IDs, variable names, and code examples remain in English.
Only user-facing text has been translated to German.
