UserAgent::getBestMatchingLangcode

public static UserAgent::getBestMatchingLangcode($http_accept_language, $langcodes, $mappings = array())

public static function getBestMatchingLangcode($http_accept_language, $langcodes, $mappings = array()) {
  // The Accept-Language header contains information about the language
  // preferences configured in the user's user agent / operating system.
  // RFC 2616 (section 14.4) defines the Accept-Language header as follows:
  //   Accept-Language = "Accept-Language" ":"
  //                  1#( language-range [ ";" "q" "=" qvalue ] )
  //   language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
  // Samples: "hu, en-us;q=0.66, en;q=0.33", "hu,en-us;q=0.5"
  $ua_langcodes = array();
  if (preg_match_all('@(?<=[, ]|^)([a-zA-Z-]+|\*)(?:;q=([0-9.]+))?(?:$|\s*,\s*)@', trim($http_accept_language), $matches, PREG_SET_ORDER)) {
    foreach ($matches as $match) {
      if ($mappings) {
        $langcode = strtolower($match[1]);
        foreach ($mappings as $ua_langcode => $standard_langcode) {
          if ($langcode == $ua_langcode) {
            $match[1] = $standard_langcode;
          }
        }
      }
      // We can safely use strtolower() here, tags are ASCII.
      // RFC2616 mandates that the decimal part is no more than three digits,
      // so we multiply the qvalue by 1000 to avoid floating point
      // comparisons.
      $langcode = strtolower($match[1]);
      $qvalue = isset($match[2]) ? (float) $match[2] : 1;
      // Take the highest qvalue for this langcode. Although the request
      // supposedly contains unique langcodes, our mapping possibly resolves
      // to the same langcode for different qvalues. Keep the highest.
      $ua_langcodes[$langcode] = max(
      (int) ($qvalue * 1000), 
      (isset($ua_langcodes[$langcode]) ? $ua_langcodes[$langcode] : 0)
      );
    }
  }

  // We should take pristine values from the HTTP headers, but Internet
  // Explorer from version 7 sends only specific language tags (eg. fr-CA)
  // without the corresponding generic tag (fr) unless explicitly configured.
  // In that case, we assume that the lowest value of the specific tags is the
  // value of the generic language to be as close to the HTTP 1.1 spec as
  // possible.
  // See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4 and
  // http://blogs.msdn.com/b/ie/archive/2006/10/17/accept-language-header-for-internet-explorer-7.aspx
  asort($ua_langcodes);
  foreach ($ua_langcodes as $langcode => $qvalue) {
    // For Chinese languages the generic tag is either zh-hans or zh-hant, so
    // we need to handle this separately, we can not split $langcode on the
    // first occurrence of '-' otherwise we get a non-existing language zh.
    // All other languages use a langcode without a '-', so we can safely
    // split on the first occurrence of it.
    if (strlen($langcode) > 7 && (substr($langcode, 0, 7) == 'zh-hant' || substr($langcode, 0, 7) == 'zh-hans')) {
      $generic_tag = substr($langcode, 0, 7);
    }
    else {
      $generic_tag = strtok($langcode, '-');
    }
    if (!empty($generic_tag) && !isset($ua_langcodes[$generic_tag])) {
      // Add the generic langcode, but make sure it has a lower qvalue as the
      // more specific one, so the more specific one gets selected if it's
      // defined by both the user agent and us.
      $ua_langcodes[$generic_tag] = $qvalue - 0.1;
    }
  }

  // Find the added language with the greatest qvalue, following the rules
  // of RFC 2616 (section 14.4). If several languages have the same qvalue,
  // prefer the one with the greatest weight.
  $best_match_langcode = FALSE;
  $max_qvalue = 0;
  foreach ($langcodes as $langcode_case_sensitive) {
    // Language tags are case insensitive (RFC2616, sec 3.10).
    $langcode = strtolower($langcode_case_sensitive);

    // If nothing matches below, the default qvalue is the one of the wildcard
    // language, if set, or is 0 (which will never match).
    $qvalue = isset($ua_langcodes['*']) ? $ua_langcodes['*'] : 0;

    // Find the longest possible prefix of the user agent supplied language
    // ('the language-range') that matches this site language ('the language
    // tag').
    $prefix = $langcode;
    do {
      if (isset($ua_langcodes[$prefix])) {
        $qvalue = $ua_langcodes[$prefix];
        break;
      }
    } while ($prefix = substr($prefix, 0, strrpos($prefix, '-')));

    // Find the best match.
    if ($qvalue > $max_qvalue) {
      $best_match_langcode = $langcode_case_sensitive;
      $max_qvalue = $qvalue;
    }
  }

  return $best_match_langcode;
}