Muti-Lingual Characters

Cha Min is heir to a very large company in Korea. After sorting out somethings, he is  going back to his work, sometimes showing off his skills to Go Se Yeon speaking in different languages on the phone to make deals. I think in this case English?

Technically everyone in Eun Seom and Tanya's village can speak 2 languages. Korean, I mean saram(or were those just people... I need to re-watch this><) and the language the people on Iark. 

Also some Saram can speak what ever the Neanthal's speak and versa-visa. (Though only in the very beginnging for the Saram)

(A show that's inexplicably in 3 parts (why Netflix?)(I'm only listing part 1 though) and will have another season coming)

Yuan Jun Cheng can speak Mandarin and Korean, though Korean is his mother tongue.

Lin Xun  can speak Mandarin and Korean, though Mandarin is his mother language. We hear a lot of Korean from the beginning when he doesn't know Jun Cheng understands Mandarin as well.

I'm pretty sure Jun Cheng's brothers can also understand Korean, but I think we only ever hear Mandarin (their mother tongue) from them.

I think Noh Sun Gi(think it was him!) was either from Japan (though looking at the name...) or was half Japanese and so could speak Japanese, and if my memory is serving me well did some.

I think... I THINK... Since our characters are in another country, even though they are on a Korean base, have to speak English or something in order to communicate with people at times... I think >.<

Yoo Yoo Jin is a famous fashion designer who has mostly lived in France, and thus, with the person who raised her after her mother's death, can and does speak occasional French.

Song Shi On has had an operation and was sent to Japan to join a secret organization and help solve difficult cases. Thus he is able to speak Japanese, he is also able to speak Korean (having originally come from Korea) and English (having studied at an university in the US), and we see him speak all three at some point, whether in flashbacks or not.

Kim Soo Hyun was raised by a Russian assassin. I don't necessarily remember him talking... but I'm pretty sure he didn't just stay quiet or only speak Korean to his adoptive father. 

I am pretty sure Heo Joon Jae speaks some English occasionally especially while there were in another country...

Shim Chung definitely speaks Korean (after a little bit of learning) and... Mermaid! ><

Tuo Wen Shuai (handsome body) holds some secrets we don't learn till later. Suffice to say, he can also speak English as well as Mandarin.

Jung Hee Joo has lived a majority of her life in Granada, Spain, and is thus able to speak Spanish fluently, and it comes in use at times. 

Due to the nature of their job, trying to sell things internationally, a lot of the characters are able to speak many different languages. Especially Ahn Young Yi who Geu Rae asks for help from in the beginning.

Eugene Choi, although he was born in Korea, came to live and grow up in the USA. Thus is able to speak English fluently, and managed to maintain his Korean. He also knows someone in the US who speaks Japanese, and so is able to speak a little of that.

This person can also speak English, though Japanese is by far his preference.

Oh Mi Joo is a translator. She translates live during interviews, as well as translated movies. She can fluently speak Korean and English. 

There are a couple of other character who can speak both, and we do hear them a little as well.

... Can someone help? Is it actually Kim Tae Ho who is speaking Spanish? or is that him using his communicator some how? Either way, Song Joong Ki is speaking Spanish.

Yang Pan Rae is able to speak both Korean and English, and uses this as a way to get into the dance team and get a little more money for her family.

I don't even have to wait for this one to end to add it (2 eps out at the time). Vincenzo understand and speaks fluent Italian, being himself Korean-Italian, and uses a lot in the very first episode. While it seems that changes to mostly "hidden" swearing and sly sentences others have no clue what he's saying. Nonetheless he's spoken a lot.

Not to mention Jang Jun Woo, from America, also speaks English when emotions get the better of him or when he wants to add emphasis.

HONORABLE MENTION

Technically, Woo Jin, because he changes bodies, can end up speaking a different language, however always understands Korean. The reason this is only a honorable mention, however, is I don't think he can actually understand the other language, though even if he can, I'm not so sure he can speak Korean at all then as his words come out in that body's mother tongue.

Amis language