Language switcher (User interface text) Block generates invalid XHTML+RDFa 1.0

A possible alternative to investigate would be a switch to XHTML+RDFa 1.1.

Good catch. switching to XHTML+RDFa 1.1 would not really help since this is basically an XML parsing issue. #2 is the way to go. I could not find any other occurrence of lang (without the leading xml:) in core. Would be good to have @alimirjamali test the patch on http://blog.mirjamali.com/

Hi. I've tested the patch and i've applied it in all my multilingual sites. It works!.

It would be nice if this patch could be committed to Drupal core to make Drupal 7 multilingual sites validate in the W3C validator.

Any progress on this issue?. The patch is really simple, works nice and fixes a Drupal core's problem which prevents Drupal multilingual sites to validate in the W3C Validator. Please, could any Drupal core's commiter review this issue and commit this useful patch to Drupal core?.

If you've reviewed and tested the patch sufficiently, please set the status of this issue to "Reviewed & tested by the community" to get it into the committer queue.

Ok, done!

This looks right to me; I guess what happened here is that when the original change was backported from Drupal 8 the difference in HTML vs XHTML wasn't taken into account.

Committed to 7.x - thanks!

Wondering if we need to revert this commit. It seems to me that this commit just swapped XHTML errors for HTML errors. When using an HTML5 doctype the W3C HTML validator throws an error:

Error: When the attribute xml:lang in no namespace is specified, the element must also have the attribute lang present with the same value.

Doesn't Drupal 7 support both doctypes? Shouldn't we be supplying both attributes?

$result[$langcode]['attributes']['lang'] = $langcode;
$result[$langcode]['attributes']['xml:lang'] = $langcode;		

Ah yes, we should be supplying both:
http://www.w3.org/TR/xhtml1/#C_7

#15 solved my validation issue using 7.43

From what I could figure out providing both indeed seems the best way.

Looks good to me, marking for Drupal 7 commit.

I tried this on http://validator.w3.org/ (with the language switcher block enabled on my local site) and it reintroduces the original bug that was fixed here - the validation error is there is no attribute "lang".

I'm not sure what to do about it - core uses XHTML+RDFa 1.0 by default so if we have to pick one to work with, it should be that (i.e. the original patch that was committed here is correct as is).

It's a real pain to ask HTML5 themes that want to validate to deal with this on their own, but I do think it's possible via https://api.drupal.org/api/drupal/modules%21system%21language.api.php/fu.... Only way I can think of to improve that would be if there is some way we can detect (or let a theme declare) what kind of doctype they are going to use, but the fix might turn out to be more complicated than the workaround.

I've faced the same problem reported in #15 too. The patch in #15 solves fixes the HTML Validation. I couldn't check if the original bug was reintroduced because of the html tag used in the theme.

I'm not sure if was a error on validator.w3.org what was reported in #20, but seems fixed now. The patch in #15 fixes the errors and does not add any extra error.

@edurenye What theme are you using for your tests? My guess is an HTML5 theme, in which case the problem would not occur there.

#20 was done using Bartik. I just tried it again now and got the same validation error I got before.

Yes, you are right, I tested it with the Zen theme. But there it fixes the error, previous to the patch I had the error, so it also occurs there.

We need a solution that works for both cases.

If it does not fix the error, then is a needs work, not a needs review.

patch 15 fixed the w3c validation error for us using a custom html5 theme.

I used the w3.org validator, before patch, language-link fails validation, after patch, clean.

I did not test Bartik though. Will take David_Rothsteins word for it.

I'd say html5 is the norm now, so maybe change the default theme in D7 core from bartik to bootstrap. (add bootstrap 7.x-3.x to core)
this could be done in the 7.60 or 7.70 new feature releases.

I came across the validation error on a search results page. For consistency it might make sense to also include both attributes in the core preprocess function as below (see comment).

/**
 * Process variables for search-result.tpl.php.
 *
 * The $variables array contains the following arguments:
 * - $result
 * - $module
 *
 * @see search-result.tpl.php
 */
function template_preprocess_search_result(&$variables) {
  global $language;

  $result = $variables['result'];
  $variables['url'] = check_url($result['link']);
  $variables['title'] = check_plain($result['title']);
  if (isset($result['language']) && $result['language'] != $language->language && $result['language'] != LANGUAGE_NONE) {
    $variables['title_attributes_array']['xml:lang'] = $result['language'];
    $variables['content_attributes_array']['xml:lang'] = $result['language'];
    
    // Also add 'lang' attribute.
    $variables['title_attributes_array']['lang'] = $result['language'];
    $variables['content_attributes_array']['lang'] = $result['language'];
  }
  //
  // snipped ...
  //
}