In order to become a citizen, you must speak English.
Whether you want to learn for your citizenship test or for other reasons, many adult schools offer very low-cost English classes. Some even prepare you for the citizenship test. Here are some local adult school programs:
Berkeley: Berkeley Adult School
Richmond: West Contra Costa Adult Education
Hayward: Hayward Adult School
San Jose: East Side Adult Education
Above is only a small list of schools. There are numerous choices for English classes through the Bay Area. You can go to this map and search for a school nearest to you home: Locate Schools