Applied linguistics covers a wide range of fields, mainly involving the interdisciplinary research between linguistics and other disciplines. The focus of applied linguistics mainly includes the following aspects:

1. Language teaching and learning: This paper discusses the objectives, methods and evaluation of language education, which is widely used in the design of various language courses and the compilation of teaching materials.

2. Language Engineering and Computational Linguistics: The technology of computer processing language information has been widely used in machine translation, speech synthesis, text classification, information retrieval and other fields.

3. Language testing and evaluation: design and develop language testing tools, such as English proficiency tests (such as TOEFL and IELTS).

4. Sociolinguistics: Study the language norms, styles and cultural differences used by different communities in society, such as dialects, spoken languages and slang.

5. Language policy and planning: analyze and formulate language policies of countries or regions, and explore the impact of language planning on social and economic development.