The language courses developed by the Foreign Service Institute (FSI) are available in the public domain. These are often repackaged and sold for beaucoup dollars (Barrons does this). But they’re free.
The best site I’ve found for downloading the materials is fsi-language-courses.org.
It has PDFs and mp3s to learn Amharic, Arabic, Bulgarian, Cambodian, Cantonese, Chinese, Chinyanja, Finnish, French, Fula, German, Greek, Hausa, Hebrew, Hindi, Hungarian, Igbo, Italian, Japanese, Kituba, Korean, Lao, Lungala, Luganda, Moré, Portuguese, Romanian, Russian, Serbo-Croation, Shona, Sinhala, Spanish, Swahili, Swedish, Thai, Turkish, Twi, Vietnamese, and Yoruba.