It is scary but true. While many Americans may take a second language, they never become fully fluent in any language they take. Because they have no one with which to converse in the second languages they tried to learn, they lose the skills to remember it, understand it, and speak it. They revert to speaking U.S. English, and that is where they are stuck.
Americans Are Not Likely to Learn Your Language First
If you come to the U.S. from another country, and you barely know some English, you will not be able to succeed in much here. Either you will need to hire an interpreter (which is expensive), or you will have to learn English as a second language. There is no way around it, given that Americans are not likely to learn your language before you learn English. Here are a few more reasons why you need to learn English.
A Lot of American Jobs Require Personal Interaction
Every job that you will be able to get when you first get a job here require that you speak enough English to be understood. That is because most of these jobs require personal interaction. You have to take food orders, answer telephones, answer questions and solve customer complaints while talking on the phone, etc.. You cannot get a job if you cannot speak enough English. That is just the unfortunate truth.
If You Are Here on an Education Visa, Your Professors and Instructors Only Teach in English
If you come to the U.S. on an education visa to attend a university here, you must also speak English. Your professors and instructors ONLY teach in English, which means you are not going to succeed in college either unless you learn English. Thankfully, foreign-born college students attending a college or university in the U.S. have an advantage. In almost every instance, you are required to take ESL classes to learn "English as a second language."
On a Positive Note
On a positive note, most Americans are willing to help you learn, understand, and speak American English. You may feel awkward at first for asking, but when you know that people will generally help you with words that are not familiar to you, it becomes less awkward. Also, the more you interact with native speakers of English, the easier it gets. If you can make friends with an American, that helps speed up your learning of American English, too.