An ED visa and a retirement visa are designed for different purposes.
An ED visa is for people who are studying, training, or joining an educational program in Thailand. In the context of Thai language learning, it is normally connected to enrollment in a recognized course. Students are expected to attend classes and follow visa conditions.
A retirement visa is for people who meet retirement-related requirements, usually including age and financial criteria. These requirements can vary depending on visa type, nationality, embassy, consulate, and current Thai government regulations.
The practical difference is simple:
An ED visa is based on genuine study. A retirement visa is based on retirement eligibility. They are not the same thing.
For future retirees, studying Thai can be a smart preparation step. But the retirement decision should still be made with the correct visa pathway in mind.