Add fr-BE and fr-LU regional language variants (similar to existing fr-CA)

[alexandrebouchez]

Summary

Please add support for Belgian French (fr-BE) and Luxembourg French
(fr-LU) language codes,
similar to the existing fr-CA (French Canadian) support.

Use Case

We develop medical practice management software used across multiple
French-speaking countries:

• France 🇫🇷 - SESAM-Vitale healthcare system, NOEMIE returns
• Belgium 🇧🇪 - eSanté platform, eAttestation, eFacturation (INAMI)
• Luxembourg 🇱🇺 - CNS eSanté, electronic mémoire d'honoraires

The documentation is 100% in French, but each country has specific
regulatory content
that should only appear for users in that region.

Current Limitation

The schema already supports regional French variants:

"language": {"enum": ["fr", "fr-CA", ...]}                                
                                                                          
But fr-BE and fr-LU are missing from the whitelist.                       
                                                                          
Requested Change                                                          
                                                                          
Add to the language enum:                                                 
- fr-BE - French (Belgium)                                                
- fr-LU - French (Luxembourg)                                             
                                                                          
This appears to be a minor change since the infrastructure already handles
 regional variants.                                                       
                                                                          
Expected Behavior                                                         
                                                                          
{                                                                         
  "navigation": {                                                         
    "languages": [                                                        
      { "language": "fr", "groups": [...] },      // France               
      { "language": "fr-BE", "groups": [...] },   // Belgium              
      { "language": "fr-LU", "groups": [...] }    // Luxembourg           
    ]                                                                     
  }                                                                       
}                                                                         
                                                                          
Benefits                                                                  
                                                                          
- Proper hreflang SEO tags (fr-BE, fr-LU)                                 
- Correct language labels in the dropdown                                 
- AI Assistant scoped per region                                          
- Clean URL structure (/fr-BE/esante/...)                                 
                                                                          
Thank you! 🙏