My car shakes between 10–25 mph when warmed up at different times. Dealer says this is normal ??
Not normal. Could be a bad tire, delaminating, or any of several other things. Take it to someone competent and responsible for inspection.
It’s definitely not normal. As @shanonia mentioned bad tire and delaminating are good suspects. Another good thing to get checked is the motor mounts. Get a 2nd opinion from an independent mechanic.
If you want to call the Dealer’s bluff, ask to test drive another 2014 Focus to see if this shake happens in all 2014 Focuses between 10-25 mph 
I don’t think this is a tire as tires generally cause vibrations in the 50 to 70 mph range. And why would it only occur when the vehicle is warmed up?
I tend to suspect a fuel or ignition problem that appears when the choke is fully off.
Or how about the lockup torque coverter?
Does your Focus have the dual clutch transmission? They’ve been troublesome. Check on some Focus forums, lots of discussion there.