Which of the following methods is the oldest for teaching English language?

The correct option is The Grammar Translation Method.

To understand why this is the correct answer, we can trace the historical origins of the methods listed:
1. The Grammar Translation Method (also known as the Classical Method): Originally used to teach classical languages like Latin and Greek, this method dates back to the 16th century and was systematically applied to modern languages like English in the 18th and 19th centuries. It is the oldest formalized method of foreign language teaching.
2. The Direct Method: Established in the late 19th and early 20th centuries as a reaction against the grammar-translation method, focusing on oral communication and avoiding translation.
3. The Bilingual Method: Developed by C.J. Dodson in the 1960s as a combination of direct method and grammar-translation techniques.
4. The Situation Method (Situational Language Teaching): Developed by British linguists (such as Harold Palmer and A.S. Hornby) between the 1930s and the 1960s.

Since the Grammar Translation Method has its roots in the teaching of classical languages dating back centuries, it is historically the oldest method among the options for teaching English.