From what i've read, it is advise to remove the nails once your bone fully consolidate.. reason is that the nail can have an effect on your bone if left inside for too long. Your bone starts to weaken and something about you losing blood cells in places that supposed to be bone, but instead is now replaced with the nails.
I believe the doctors and nurses do speak some English. I have been in contact with them recently through emails, and all of our communications have been through english.
In regards to the physiotherapist, the doctor there told me that you need physical therapy throughout the lengthening process, they charge 20USD per session if you want their specific experience leg lengthening physical therapist (with 10 years of experience in leg lengthening therapy) to come visit your home and work with you through the physical therapy. Or you can pay for their all inclusive package which is 10,500 USD, where they cover your stay, meal, physical therapy, doctor access, medicine, x-ray fee or any sort of accommodation you need. This package is a 3 months deal.