get_locale_for_key
Description:
[ Version ( since = "2.56" ) ]
public string? get_locale_for_key (string group_name, string key, string? locale = null)
  public string? get_locale_for_key (string group_name, string key, string? locale = null)
Returns the actual locale which the result of get_locale_string or get_locale_string_list came from.
If calling get_locale_string or 
      get_locale_string_list with exactly the same 
      this, group_name, key and locale, the result of those functions will 
      have originally been tagged with the locale that is the result of this function.
Parameters:
| this | 
           a KeyFile  | 
      
| group_name | 
           a group name  | 
      
| key | 
           a key  | 
      
| locale | 
           a locale identifier or null  | 
      
Returns:
| 
           the locale from the file, or null if the key was not found or the entry in the file was was untranslated  |