according to this page https://wiki.sourcefabric.org/display/NsLingo/List+of+Articles you are using keyword constraint correctly, but maybe your list is in context that doesn't see that exact article. Try adding ignore_issue="true" and ignore_section="true" to list_articles and see if some results are shown
-- Ljuba Rankovic Senior Front End Developer, Sourcefabric ljuba.rankovic@sourcefabric.org