Hamed, there are so many variables to consider. Experience, where one lives, demand, whether one is an independent personal trainer or works in gym.
Personally, I believe if you are bilingual you have a greater earning power.
One of things I am working on is offering personal training courses to to the spanish speaking community as there is a need and we don’t see many personal trainers of latino background.
I really hope you decide to enter the industry. According to the Bureau of Labor Statistics there is an expected growth of 29% in the health and fitness industry up until 2018.
Feel free to contact me if you have any questions.