Posts. Add lang in permalink when render text post

When render a post using a TOC (.. contents::), the table links are wrong when site is multilingue, because links don't added locale (using default language).

Example where I patched and publish this feature:

* spanish: http://www.zzsaas.com/es/preguntas-frecuentes.html
* catalan: http://www.zzsaas.com/ca/preguntes-frequents.html