For the tooltip of a xammap I cannot take the greek character encoding. I have set UserControl.Language = "el" (for Greek language). I have tested the shapefile with ArcExplorer and I saw that the map has, indeed, greek characters.
Hi iliaspantoleinas,
Unfortunately silverlight support a small set of character encodings, please take a look at the following pages: http://msdn.microsoft.com/en-us/library/system.text.encoding(v=VS.95).aspx, http://msdn.microsoft.com/en-us/library/t9a3kf7c%28VS.95%29.aspx. I will recommend to change shapefile character encoding to UTF8.
Regards,
Ivan Kotev