In the iCal ontology , you attach range 'xsd:string' to many
properties, such as 'ical:description' and 'ical:comment'. Although the
range is suitable for properties such as 'ical:tzname', etc., such a
range is not suitable for properties with prose text values as it
precludes the usage of language tags. A literal with a language tag
cannot be a member of 'xsd:string' (see  for discussion), and many
people use properties such as 'ical:description' with language tags.
Perhaps the easiest and best solution would be to remove the
'xsd:string' range constraint from such prose-text properties.