There are two writing systems in use for Mongolian. In Mongolia, the Cyrillic alphabet is used and is presented on this page. In the Inner Mongolian region of Mainland China, the traditional Bichig alphabet is used and has its own page here. In 2025, Mongolia will begin a five-year transition period to change from Cyrillic to Bichig as the primary writing system.
Бөгжний Эзэн (Mongolian [Cyrillic]), purchased on-line from Internom.mn, Ulaanbaatar in 2024, 2025 (hardback)
Tolkien, J.R.R., Бөгжний Эзэн, trans. by B. Amarbayasgalan (Monsudar, 2024), 1, Бөгжний Барилдлага. ISBN: 978-9919-28-115-1
——, Бөгжний Эзэн, trans. by B. Amarbayasgalan (Monsudar, 2025), 2, Хоёр Аранга. ISBN: 978-9919-28-178-6
——, Бөгжний Эзэн, trans. by B. Amarbayasgalan (Monsudar, 2025), 3, Хаан Эргэж Ирсэн Нь. ISBN: 978-9919-28-247-9
This was one of the most recent languages to be added to my collection. I couldn't find a copy anywhere. Out of the blue in April of 2024, a Tolkien collector from Mongolia, Adiyasuren Jamiyandagva, contacted me by email after seeing the home page here where I (formerly) mentioned that I was only lacking a copy of the translation into Mongolian. He pointed me to the publisher of this brand new translation (FR just published in the last week of March 2024). I had ordered it within 24 hours (much less, actually) of his email.
There was a previous translation into Mongolian from Russian in 2009. The published version of this translation is very rare, but a complete 909-page pdf of the translation itself can be found at: scribd.com.