Is there a Thai visa for learning the language that allows long-term stay?

Yes, there is an education (ED) visa that allows you to stay in Thailand while studying the Thai language at an approved school. You can initially receive a 90-day visa, which can be extended every 90 days for up to 15 months, as long as you maintain your enrollment and attend classes as required. Schools typically require a minimum of 10 hours of language study per week to comply with immigration rules, and they often have module-based programs of 3 hours per day, 5 days a week.