The United States does not have an official language, yet English is the country's primary language. Due to the diversified nature of the United States, you will hear a wide selection of foreign languages.
The language of instruction in American universities is English. As part of your application, you will very certainly be expected to present proof of your English language skills. The level of language proficiency you achieve will be determined by where you study. It is typical for colleges to offer English language classes to help you improve if you do not reach the acceptable standards for your course.
If English is not your first language, you should take advantage of the opportunity to learn a new language while you study. Practicing with locals and other students is an excellent approach to do so. Having advanced English skills is an excellent talent to have on your CV or resume.