My question involves a child custody case from the State of: CA

I am a divorced man and father of a 9-year old girl.
I am originally from France but I have been living in California for 15 years and I am a US citizen. My daughter was born in California.
I now have been divorced for 5 years.

The initial agreement between my ex-wife and myself was 50/50 physical & legal custody, with no child support involved.

However for the past 4-5 years my daughter's mom has been struggling with addiction (heroin mainly) and has been in detox/rehab/sober living pretty much non stop.
She has been arrested for drug possession and under the influence multiple times.
About 18 months ago there was a domestic violent incident between my ex-wife and her new husband and my daughter was present. Again, drug charges were filed.
Shortly after that I was contacted by Child Protection Services regarding the incident and other prior reported incidents and they urged me to seek full custody as my ex-wife has become a danger for her own daughter (CPS's own words). CPS went to my daughter's school as part of their investigation and my daughter described to them how she witnessed her mom shooting heroin (with a syringe) in front of her.
This was devastating for me as I didn't know the extent of the damages.

For the past 18 months I have been taking care of our daughter all by myself. I now have full legal and physical custody but I do not receive any child support since mom is obviously not able to work and is now on disability. She has been in rehab & sober living again since April of 2015. I just found out that she has been arrested again last week and charged with the following:
- 11350(A) HS POSSESS NARCOTIC CNTL SUB
- 11550(A) HS UNDER INFLUENCE CNTL SUB
I believe that this time she faces a jail sentence.

I feel extremely isolated here in the US and I am considering moving back to France for a few years and with my daughter, so that I can get help from my family and friends there, and have more time for my daughter.
My daughter is pretty excited at the idea of moving to France one day. We spent the whole last summer there and she bonded with ever person in my family.

I want to know what are my chances to have the court approve such a decision.
Again, moving to France would only be temporary. 1 year or maybe 2 years at most so that my daughter can be safe and have a some peace, far away from the drama her mom has put herself into.
For me, as a single dad, it would make a significant difference as I will have a entire support system there, which would also be very beneficial to my daughter.

If a court doesn't approve my request which I would understand, I always have the option to talk my-ex wife into it and to come to a mutual agreement.

Thanks!