Stir together the cabbage, mayonnaise, yogurt, half the lime juice, and a pinch of salt. Chill while you prepare the fish.
Heat about 1/2 inch of neutral oil in a heavy skillet to 350°F (175°C). Pat the fish dry and season with the remaining salt and smoked paprika.
Whisk the flour, cornstarch, baking powder, and a pinch of salt. Whisk in the cold beer or sparkling water just until a few small lumps remain.
Working in batches, dip the fish in batter and fry for 2 to 3 minutes per side until golden and opaque; check thick pieces for 145°F (63°C). Drain on a wire rack.
Warm the tortillas in a dry skillet. Fill with fish and cabbage slaw, finish with lime, and serve right away.