function language_from_browser

Identify language from the Accept-language HTTP header we got.

The algorithm works as follows:

• map browser language codes to Drupal language codes.
• order all browser language codes by qvalue from high to low.
• add generic browser language codes if they aren't already specified but with a slightly lower qvalue.
• find the most specific Drupal language code with the highest qvalue.
• if 2 or more languages are having the same qvalue, respect the order of them inside the $languages array.

We perform browser accept-language parsing only if page cache is disabled, otherwise we would cache a user-specific preference.

Parameters

$languages: An array of language objects for enabled languages ordered by weight.

Return value

A valid language code on success, FALSE otherwise.

File

drupal/core/modules/language/language.negotiation.inc, line 84

Language negotiation functions.

Code

function language_from_browser($languages) {
  if (empty($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
    return FALSE;
  }

  // The Accept-Language header contains information about the language
  // preferences configured in the user's browser / 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"
  $browser_langcodes = array();
  if (preg_match_all('@(?<=[, ]|^)([a-zA-Z-]+|\\*)(?:;q=([0-9.]+))?(?:$|\\s*,\\s*)@', trim($_SERVER['HTTP_ACCEPT_LANGUAGE']), $matches, PREG_SET_ORDER)) {

    // Load custom mappings to support browsers that are sending non standard
    // language codes.
    $mappings = language_get_browser_drupal_langcode_mappings();
    foreach ($matches as $match) {
      if ($mappings) {
        $langcode = strtolower($match[1]);
        foreach ($mappings as $browser_langcode => $drupal_langcode) {
          if ($langcode == $browser_langcode) {
            $match[1] = $drupal_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]) ? (double) $match[2] : 1;
      $browser_langcodes[$langcode] = (int) ($qvalue * 1000);
    }
  }

  // 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($browser_langcodes);
  foreach ($browser_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 occurence 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 occurence of it.
    $generic_tag = '';
    if (strlen($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($generic_tag) && !isset($browser_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 browser and Drupal.
      $browser_langcodes[$generic_tag] = $qvalue - 0.1;
    }
  }

  // Find the enabled 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;
  $max_qvalue = 0;
  foreach ($languages as $langcode => $language) {

    // Language tags are case insensitive (RFC2616, sec 3.10).
    $langcode = strtolower($langcode);

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

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

    // Find the best match.
    if ($qvalue > $max_qvalue) {
      $best_match_langcode = $language->langcode;
      $max_qvalue = $qvalue;
    }
  }
  return $best_match_langcode;
}