I don't know if this will get you there - http://www.allezhop.de/frysk/wb.htm dictionaries, Frisian to various languages. Caution: Flaak doesn't seem to be a Frisian name. If you mean a surname there are no Flaaks in Holland and just a few in Northern Germany. The German bearers are not located in East Friesland, which is German Friesland. The surname Flaak may be related to the surname Flack, meaning unknown, but thought to have something to do with water, as you suggest for Flaak.