"Still water run deep" is a quote that put in value the toughness and dangerousness of the most quiet, the silent people. So, you might translate it as "Fin zok nahlot mun aal hind dinokiil.", literally "The most silent man could wish your death".

"However long the night, dawn always breaks", not actually in need of explanation, could be translated by "Lingrah vulon drun lot vu" , "A long night bring a great dawn", or another "Zok vul suvulaan, zok viin shul", "The darker (is) the twilight, the most shining (will be) the sunlight"