fix(i18n): add axios dependency and fix DeepL API parameters
- Install axios for DeepL HTTP requests
- Remove unsupported preserve_formatting parameter from DeepL API calls
- Add formality parameter only for supported languages (DE, FR, etc.)
- Tested successfully: 'Hello, World!' → 'Hallo, Welt!'
DeepL API Status:
- API key configured (free tier: 500k chars/month)
- Current usage: 12,131 / 500,000 characters (2.43%)
- Remaining quota: 487,869 characters
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Co-Authored-By: Claude <noreply@anthropic.com>