When you mail oversees do i write in the language to the country going to or the country coming from or both

Question

For example im mailing something from US to Mongolia

do i

write in English or Mongolian

write from in english to in mongolian

write in both

Answer 1

No you can write it in English most all Mongolians speak, read and write in English. I don't know what they tell you in the US but everyone around the world  can read and speaks basic English.

Answer 2

You write in the Language of the person who is going to read the letter.