setLocale method
- Locale locale
 
setLocale is a function that takes a Locale object as
a parameter and sets the _locale variable
to the value of the Locale object
Args: locale (Locale): The locale to be set.
Returns: The current locale.
Implementation
void setLocale(Locale locale) {
  if (!_languages.contains(locale)) {
    return;
  }
  _locale = locale;
  notifyListeners();
}