Route 66 deletes self referential hreflang tag

Hi !

When the plugin is activated and the languagefilter plugin is activated the lines
<link href="https://www.xxx.com/en/" rel="alternate" hreflang="en-EN" />
<link href="https://www.xxx.com/de/" rel="alternate" hreflang="de-DE" />
<link href="https://www.xxx.com/pl/" rel="alternate" hreflang="pl-PL" />

will read

<link href="https://www.xxx.com/de/" rel="alternate" hreflang="de-DE" />
<link href="https://www.xxx.com/pl/" rel="alternate" hreflang="pl-PL" />
<link href="https://www.xxx.com/en/" rel="canonical" />

so

<link href="https://www.xxx.com/en/" rel="alternate" hreflang="en-EN" />

gets deleted.

Correct behaviour would be

<link href="https://www.xxx.com/en/" rel="alternate" hreflang="en-EN" />
<link href="https://www.xxx.com/de/" rel="alternate" hreflang="de-DE" />
<link href="https://www.xxx.com/pl/" rel="alternate" hreflang="pl-PL" />
<link href="https://www.xxx.com/en/" rel="canonical" />

in the header.

Yes, the error/deletion goes away when disabling the plugin. I haven't looked enough into this , but i think the addheadlink funtion just takes one line per URL and deletes other entries if multiple calls are made. i hacked into languagefilter.php
$doc->addHeadLink($server .'/' . $languages[$this-&gt;current_lang]->sef.'/' , 'alternate', 'rel', array('hreflang' => $this->current_lang));
-> gets also deleted
$doc->addCustomTag('<link href="https://www.firecoders.com/' . $server . '/'.$languages[$this-&gt;current_lang]->sef.'/' . '" rel="alternate" hreflang="'.$this->current_lang.'" />');
-> stays
If I would guess you need to call addCustomTag instead of addHeadlink for the canonical tag ?