Rangjung Yeshe Institute is accredited as part of Kathmandu University, and just received a new batch of funding from the Khyentse Foundation to make further improvements to their programs.
Most of the staff who were working there when I attended the Beginning Colloquial Tibetan course back in 2010 are no longer there, and it is quite a bit expensive compared to other programs in Nepal & India, but not many have the same amount of clout as they do. They are very used to working with students of foreign universities.
RYI is the shedra/language learning branch of Ka-Nying Shedrup Ling, Chökyi Nyima Rinpoche's monastery in Boudhanath. The Boudha locals call it simply "the White Gompa." At one point an old Tibetan man approached me while I was doing kora around the Jarung Kashor (Boudha Stupa) and asked me if I was studying there. When I told him yes, he gave me a lovely creme-colored kata. Folks there are very appreciative of Westerners' efforts to help propagate the Dharma.
If you're looking for the most economical Tibetan language program abroad, it's Manjushree Centre in Darjeeling, hands down. Nine months of study with them costs a paltry $480 in tuition, and they're a secular institution affiliated with the Tibetan Government-in-Exile as far as credentials go. That said, I haven't studied there so I can't comment as to the quality.
A kind of middle ground between those two is the new Namo Buddha program starting it's first class in Beginning Tibetan as of June 2014. The chances of you getting direct credit from your university thru them are slim, as they're just starting off and are a religious institution, but the opportunity to study directly under the Gyalwang Karmapa's main translator for the Kagyu Mönlams (Ven. David Karma Choepel) may be too tempting to pass up, especially if your professor can examine you upon your return and give you credit based on demonstrates competency. If you're interested in this one, PM me. They're limiting the first class to a mere 10 students.
Then there are distance learning courses thru places like Esukhia and Lama David Curtis' Tibetan Language Institute, though they are self-study oriented. Of the two, TLI has been around much longer and is run by a long-time student of the late Kyabjé Kalu Rinpoche who completed 3 year retreat, but Esukhia is making some good headway with prominent organizations and translators in the short time they've been around, and has a more academic approach.
"The Sutras, Tantras, and Philosophical Scriptures are great in number. However life is short, and intelligence is limited, so it's hard to cover them completely. You may know a lot, but if you don't put it into practice, it's like dying of thirst on the shore of a great lake. Likewise, it happens that a common corpse is found in the bed of a great scholar." ~ Karma Chagme དྲིན་ཆེན་རྗེ་བཙུན་བླ་མ་རཱ་ག་ཨ་སྱ་མཁྱེན་ནོ།