def convert_language_code_to_iso639_2(lang_code):
    """
    Translate OpenSubtitle language code to its iso-639-2 equivalent.

    OpenSubtitles seem to support some extensions to iso-639-2, for instance
    "pob" means "brazilian portuguese".

    See http://www.opensubtitles.org/addons/export_languages.php.

    :param str lang_code: original language code from OpenSubtitles
    :return: iso-639-2 compatible
    """
    return {
        'pob': 'por',
        'pb': 'por',
    }.get(lang_code, lang_code)