Is it permissible to complete the acquisition of experience from nuns of a French church who receive a small fee for teaching communication and accent in the French language, knowing that the meeting place resembles an educational institute and there is a cross in the building's courtyard?

It is not forbidden to enter a place with a cross to acquire permissible knowledge. This is even more permissible than entering a church itself. However, consideration must be given to the possibility of the questioner being influenced by the Christian environment and the resulting religious prohibitions. If she is safe from that, then there is no harm in her continuing.