Well, in fact, the authors declare Unicode support, but there is none.
After having chosen language settings, no charset definition has been set in tested skins. So the browser uses the US-ASCII encoding (XHTML default setting). Additionally, even if you set a Unicode encoding (there is something described as “pl_PL-utf-8”), the administration panel uses US-ASCII and replaces every non-ASCII character by an HTML entity in numeric format (ie. ê) - and this entity is then passed to the database and displayed. And the database charset setting is consequently 'latin1', not 'utf-8'.