<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def localeselector():
 """Default locale selector used in abilian applications."""

    # if a user is logged in, use the locale from the user settings
    user = getattr(g, "user", None)
    if user is not None:
        locale = getattr(user, "locale", None)
        if locale:
            return locale

    # Otherwise, try to guess the language from the user accept header the browser
    # transmits.  By default we support en/fr. The best match wins.
    return request.accept_languages.best_match(
        current_app.config["BABEL_ACCEPT_LANGUAGES"]
    )