One can improve one's English pronunciation a few ways. One way could be taking classes at a local college or online which training videos and guides.

we can improve our spoken language by talking to a native person frequently ，practicing listening and reading more.

Everyday speak to as many people as you can. You can only improve spoken English by speaking and it is better to speak to people than speak to yourself.

American English is the English spoken in the United States, which differs in some ways from English spoken in Britain and other countries.

A corpus is a database of spoken or written language.

The words in a corpus can be collected from a variety of sources.

For example, words in a written corpus may come from newspapers, magazines, books, or the internet; while words in a spoken corpus may come from everyday conversations.

With computer software to analyze a corpus, we can find out the most commonly used English words, expressions, and phrases in a language.