Function detect_system_locale 

pub fn detect_system_locale() -> Option<String>

What: Detect system locale from environment variables.

Inputs:

• None (reads from environment)

Output:

• Option<String> containing locale code (e.g., “de-DE”) or None if not detectable

Details:

• Checks LC_ALL, LC_MESSAGES, and LANG environment variables in order
• Parses locale strings like “de_DE.UTF-8” -> “de-DE”
• Returns None if no valid locale found