The Fiasco Theater production of Twelfth Night is energetic, clearly spoken and firmly middle-of-the-road. The company, with standard members, must try to cast every actor in a part, even if the requirements are slightly off. In Shakespeare’s story of twins, a brother and sister, who are shipwrecked in a foreign country, Illyria, where they have amorous mix-ups before they are reunited, an audience may notice that Emily Young’s slender Viola bears little resemblance to Javier Ignacio’s chunkier Sebastian, apart from wearing glasses and a ribbed, russet sweater, though it’s unlikely that will spoil one’s enjoyment.