Read the passage.
Supporting Biliteracy
There are many good reasons to learn a second language. A second language can improve your understanding of your native language, open the door to new job opportunities, and help you learn about other cultures. Yet American students are less likely than European students to study foreign languages in school. To address this gap, several states have begun doing more to encourage biliteracy—the ability to read and write in two languages. California, New York, and Illinois are among the states that have passed laws establishing a state "Seal of Biliteracy." A Seal of Biliteracy shows that a student has achieved proficiency in a second language. Supporters of the seals say that they honor the importance of second-language learning. The seals also provide colleges and future employers with evidence of students' abilities.
What is the main, or central, idea of the passage?