What should I do if I am randomly checked and cannot speak English when I go through customs when traveling to the UK?

Just shake your head and say no. You don’t need to know the language of the other country for a tourist visa.

The characteristics of a tourist visa are: the purpose of visit is tourism, and the validity period and stay period of the visa are relatively short. (Most are valid for 90 days, with a stay period of 30 days. Individual embassies will grant fixed-term tourist visas based on the applicant’s specific stay dates: such as Germany, Australia, etc.). Holders of tourist visas cannot engage in work, business or other activities unrelated to tourism in the destination country, let alone illegal activities.

Extended information:

With the development of world globalization and the continuous advancement of transportation technology, the world tourism market continues to grow. It is foreseeable that tourist visas will become more common and convenient. It has become another major form of visa. Many countries specifically issue tourist visas to tourists in order to promote local tourism.

Tourist visa is one type of visa. Some countries issue tourist visas specifically for tourists, namely: "touristvisa". The characteristic of tourist visa is that the period of stay is short, usually 30 days, the longest is 90 days, and generally cannot be extended. Those holding a tourist visa cannot work locally or engage in activities unrelated to tourism. Group tourist visa is a type of tourist visa. Its characteristic is that the visa is not printed on the passport. Tourists must enter and exit the country as a group.

Baidu Encyclopedia-Tourist Visa