Ya lo he encontrado, el fichero README del directorio "/filter/multilang/" esta explicado.
Disculpen... a veces no leo suficiente.
Angel AG
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This filter implements an XML syntax to provide
fully multilingual website. No only the Moodle interface
can be translated but also the content!
To activate this filter, add a line like this to your
config.php:
$CFG->textfilter1 = 'filter/multilang/multilang.php';
Syntax to display a multilingual content:
<lang lang="en" format="auto">
Introduction
</lang>
<lang lang="es" format="auto">
Introducción
</lang>
<lang lang="de" format="auto">
Einleitung
</lang>