I never counted, but I think I have as many right turns as left turns. So signaling on left arm and right arm is 50/50.

I know some people do the old signaling (from where cars didn't have blinkers where car drivers signaled out of the left window with an "L" to go right).

But stretching out to the right when signaling right will make sense to everyone behind you (none of the car drivers behind me was alive when cars used hand signals for indicating). Actually in the US I saw for the first time signaling to go to the right by using the left arm... so that is not an international standard or something you can count on people to know.

Indicating to the right with right arm when intending to go right is how I learned it and how I have always seen it in Germany. When going to the left, the same with the left arm. The car driver behind you does not need to be trained or guess where you intend to go. When you do everything with the left arm, people that are not "initiated" in this secret ritual won't know that you intend to go right. Also imagine a bike lane between two drive lanes (like for bus lanes on the right). When you want to go right in front of the bus on the right to you, that driver will be alerted by you stretching your arm into his lane. He does not care about your left arm signals, but your right arm will indicate to him you are about to cut into his lane.