2009 Mitsubishi Galant my car stoped running

see if you can turn it over by hand or wrench that will be a start. if you can turn it over try another mechanic

They turned it on said it could be my timing belt he said my transmission oil is black that's bad right

yes black trans oil means that something inside the trans like seals are totally gone. as for timing belt if you haven't damaged any valves in the future belts should be replaced at 60k along with tensioners. same for belt for alternator. Unless you are in California then it's 105k

What does that mean for my transmission? New one can it be fixed?

it means the trans will probably have to be rebuilt happens all the time.

Is mitsubishi harder to fix than other cars

not really but may be more expensive due to parts coming from japan.

It's so hard finding a mechanic I need a proper diagnosis cuz that other mechanic is so not good is it possible if the timing broke that the pistons came lose and are hitting the motor n that can be replaced?

if your belt broke and you have an interference motor then you probably bent valves and need the valves and or cylinder head replaced. you might check in your area for auto repair that have a good rating an d have them re diagnose your car.if you know of someone who has had good service at a place then you might have it towed there.

It is an interference motor I looked it up but if it is that it could be fixed without replacing the whole motor
?

yes it could thought I explained that