The individual alien people visiting Earth study for their missions, and this includes human languages as well as each other's languages.
Besides this, telepathy does not always necessarily have to be in a specific language.
I hear audibly by telepathy in voice and it's usually in my own language.
However, sometimes I hear them speaking in their own languages telepathically and my mind translates it.
Also, sometimes some of the races speak to me aloud in physically vocal voices, either in my language or in theirs.
My husband's natural abilities to communicate with many different races far exceeds my own.
Not all races can physically produce the language sounds of another particular race but this is no barrier to hearing or understanding telepathically.
Human Alien Communication
A human who has alien contact can communicate with his alien contacts whether he is physically aware of doing so or not.
Practicing meditation is one way of helping ourselves become aware of all that we do spiritually, including meeting with and communicating with alien life.
Humans who do not have alien contact may have great spiritual abilities of communication and of spiritual awareness, but they will not have direct, personal contact or communication with alien life.
This is because the alien people are only allowed to approach and work with their own related, willing humans.
Although these subjects of alien life and crafts are certainly relevant to our entire race, and any human may witness sightings of alien crafts and/or help spread education about alien life visiting our world.