static getBase(lang) {
    const LanguageUtils = shaka.util.LanguageUtils;

    const splitAt = lang.indexOf('-');
    let major;

    if (splitAt >= 0) {
      major = lang.substring(0, splitAt);
    } else {
      major = lang;
    }

    // Convert the major code to lower case. It is standard for the major code
    // to be in lower case, but it will also make the map look-up easier.
    major = major.toLowerCase();
    major = LanguageUtils.isoMap_.get(major) || major;

    return major;
  }
Get the normalized base language for a language code.

@param {string} lang
@return {string}
@export