Here's a short story:

The Yuan dynasty (Chinese: 元朝; pinyin: Yuán Cháo), officially the Great Yuan (Chinese: 大元; pinyin: Dà Yuán; Mongolian: Yehe Yuan Ulus[a]), was the empire or ruling dynasty of China established by Kublai Khan, leader of the Mongolian Borjigin clan. Although the Mongols had ruled territories including today's North China for decades, it was not until 1271 that Kublai Khan officially proclaimed the dynasty in the traditional Chinese style. His realm was, by this point, isolated from the other khanates and controlled most of present-day China and its surrounding areas, including modern Mongolia and Korea. It was the first foreign dynasty to rule all of China and lasted until 1368, after which its Genghisid rulers returned to their Mongolian homeland and continued to rule the Northern Yuan dynasty. Some of the Mongolian Emperors of the Yuan mastered the Chinese language, while others only used their native language (i.e. Mongolian) and the 'Phags-pa script. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: What is the official name of the Yuan dynasty?
Guess: Great Yuan

Question: How would you say that in Mongolian?
Guess: Yehe Yuan Ulus[a]

Question: Was it an empire?
Guess: yes

Question: In Russia?
Guess: No

Question: Where?
Guess: China and its surrounding areas, including modern Mongolia and Korea.

Question: Who started it?
Guess: Kublai Khan

Question: Was he the head of a Mongolian clan?
Guess: yes

Question: Did he state the existence of the empire in the eleventh century?
Guess: yes

Question: What year exactly?
Guess: 1271

Question: Did his empire have a lot of interaction with other cultures?
Guess: no

Question: Would modern day Korea have been part of this area?
Guess: yes

Question: What about France?
Guess: No

Question: What was unique about this empire?
Guess: It was the first foreign dynasty to rule all of China and lasted until 1368

Question: Who went back to Mongolia after this?
Guess: Genghisid rulers

Question: Did they still control some areas?
Guess: yes

Question: What was that empire called?
Guess: the Northern Yuan dynasty

Question: Did any of them speak English?
Guess: Not that's mentioned

Question: Did any of them speak Mongolian?
Guess: yes

Now answer the following question in the same format.

Question: Why would they have known how to speak that?

It's their native language