Taxes are filed between January 1-April 15.
Many countries have a tax treaty with the United States.
International students are not required to pay Social Security or Medicare taxes. These are programs American citizens pay into in preparation for their retirement. Since the regular paycheck will stop at retirement, this is a form of income. Each year the Office of International Student Retention Services invites the IRS in to give a tax information workshop. This is the root of the word salary.