To be able to use a particular language
The man can speak English and Russian.
To be able to speak a language
I know some French.
To know the meaning of words, a language, what someone says, etc.
I can understand Chinese.
He uses Spanish when he talks with his parents.
Make yourself understood
To communicate effectively
I tried to make myself understood to the customs officers with some English words I know at Kennedy International Airport.
A person who speaks a particular language
The man is a Spanish-speaker.
Able to speak or write a foreign language very well
She became fluent in German.
Able to do something well or skillfully because of training and practice
She is proficient in German and Chinese.
Able to speak two languages equally well
My children are bilingual in English and Vietnamese.
Able to speak three languages equally well
I am trilingual in English, Spanish and Italian.
Speaking, using, or written in several different languages
Some people in my office are multilingual.