Remember that a QName like dbpedia:whatever
is just an abbreviation for a complete URI. This works:
select ?label {
<http://dbpedia.org/resource/Marit_Bj%C3%B8rgen>
dbpedia-owl:birthPlace
[ a dbpedia-owl:Country ;
rdfs:label ?label ]
filter langMatches(lang(?label),"en")
}