Learning any type of foreign language can be hard, but especially for Mongolian language, it can be even moreso difficult for someone who is not used to Mongolic languages.
Contrary to many people’s belief, Mongolian doesn’t share any similarities with Mandarin Chinese nor Russian as its a separate language on its own with its own unique qualities. The closest languages to Mongolian are Buryat, and Kalmyk. You could even say they are a dialect of the Mongolic language as a whole.
So unless you are at least somewhat experienced with other Mongolic languages, it will be hard to fully master the Mongolian language / Khalkha dialect (which is the most commonly spoken in the world).
Why Is It So Hard?
It’s not necessarily that the alphabet or the grammar that are hard to to learn, but it’s the lacking amount of available resources. It’s very hard to come across quality textbooks that teach Mongolian in English or other common languages.
While I do have a basic introductory course for Mongolian, the intermediate and advanced level of grammar are difficult to teach. Most teachers who are qualified to teach upper level Mongolian rarely speak English, so there just isn’t enough qualified tutors and teachers for the world.
Other Challenges With Learning Mongolian
Aside from that, accent / pronunciation is THE most common challenge a lot of people learning Mongolian have. The sounds in Mongolian language are very different from most common languages around the world.
It’s very throaty and harsh while at the same time soft and harmonious. There subtle vowel sounds in the middle or the end of words which can completely change the meaning of the word.
However, from my personal experience almost everyone has difficulty pronouncing the Mongolian Л sound.
Also, the rules and spelling for words keep changing from time to time by the government, hence the educational system has to play catch up with such changes. You can check if certain spelling is correct or wrong here: http://spellcheck.gov.mn/