The foreign language instruction requirement ruling was in a case in California and involved Chinese students.    It applies to all Foreign Language speakers,

Lau v. Nichols (1974)

https://supreme.justia.com/cases/federal/us/414/563/case.html

"The failure of the San Francisco school system to provide English language instruction to approximately 1,800 students of Chinese ancestry who do not speak English, or to provide them with other adequate instructional procedures, denies them a meaningful opportunity to participate in the public educational program, and thus violates § 601 of the Civil Rights Act of 1964, which bans discrimination based "on the ground of race, color, or national origin," in "any program or activity receiving Federal financial assistance," and the implementing regulations of the Department of Health, Education, and Welfare."

"We do not reach the Equal Protection Clause argument which has been advanced, but rely solely on § 601 of the Civil Rights Act of 1964,"