How do you say "Welcome to English", as in welcome to English class? How do you say "Welcome to English", as in welcome to English class?
If it is a title of a book, it can be translated as  "英語入門"

If it is a greeting from a teacher to his class, it means " 歡迎第一次學習英語。" = "Welcome to English learning for the first time." 

Beside the above examples, the phrase " Welcome to English" doesn't provide enough context to be meaningful.