gistfile1.txt

def detect_language(request):
    """
    Pick a user's preferred language from their Accept-Language headers.
    """
    accept = request.META.get('HTTP_ACCEPT_LANGUAGE')
    if not accept:
        return ''

    ranked_languages = parse_accept_lang_header(accept)
    for lang, q in ranked_languages:
        locale = to_locale(lang).replace('_', '-')
        if locale in product_details.languages:
            return locale
        shortened_locale = locale.split('-')[0]
        if (shortened_locale != locale and
            shortened_locale in product_details.languages):
            return shortened_locale

    # No dice.
    return ''