"Closed training" is training that restricts freedom and prevents contact with the outside world. A fully enclosed school means that daily life, such as eating, studying, exercising and sleeping, is in the school. You can only leave the school on the day when the school stipulates to go home on holiday.
Language is a tool for people to communicate, a skill, not just knowledge of learning and research. The purpose of learning English is to communicate. "English is not learned, it is used." Language learning can't be done overnight, once and for all. It takes a lot of practice to master it skillfully. In the simulated language environment, teachers use various methods other than translation to teach intuitively, so that students can form the habit of thinking in English from the beginning, thus improving their comprehensive English application ability.
If you really want to master a foreign language, you should forget your mother tongue for a while. Many learners are used to switching between Chinese and English to learn English, which seriously hinders the habit of cultivating English thinking.