Writing multi-cultural, biracial, multi-racial, bi-nationality, etc.
I see this a lot, but I wanted to address this for anyone to see. This is Asian-related, since AFF is an Asian-based fansite.

When writing someone who is not just one race, nationality (ex. Korean-American, Chinese-American, Korean-Chinese, etc), and they have lived in both cultures, or speak both languages, they may still get confused on their culture skills, language skills. Not like "Oh, sorry, I forgot I'm in China and I'm speaking Korean hahaha" No. Also, Koreans who speak English (or biracials that speak it) will speak Konglish.

If your pairing has one half of a family that is foreign to the culture and lives away, or is adapting to the culture, that needs to be shown. Your character's love interest may not speak English, Chinese, Japanese, etc., and may have to rely on your character to translate. They may disagree with their culture styles or their opinions. They may even help teach the relative the native language.

Examples of biraces.

 

Mixed Nationalities; this means that they have a residency card in said countries. This is only for mixed nationalities (full bloods under different nations) and not biracial celebs.

American 미국: They speak English, may speak other languages, probably have American mannerisms, used to provacative culture.
Kim Dani (MBK, PD101)
Cheska Ahn (fmr Fiestar, solo)
Ailee
Jessi Ho
Tiffany Hwang (SNSD)
Sunny Lee (SNSD; she was born there, so she is a resident)
Jessica Jung (fmr SNSD, solo)
Krystal Jung (f(x))
Amber Liu (f(x); Taiwanese)
Bekah Kim (fmr AS)
Joshua Hong (Seventeen)
Bobby Kim (ikon, solo)
Park Bom
esNa / Yoon Bitnara
Nicole Jung (fmr KARA, solo)
Taecyeon Ok
Jay Park
Park Jaehyun / Jae (Argentina born, raised in Cali; DAY6)
Mark Tuan (CH)
Kim Euna / Kim Yuna (fmr The Ark, Unpretty Rapstar)
Park Tina (fmr Blady)
Megan Lee
Grace Kim (Unpretty Rapstar)
Ns Yoon G / Kim Christine

Canadian캐나다: May know some French, speaks English, used to Canadian mannerisms, probably used to provactive culture.
Henry Lau (Chinese)
Wendy Son
Mark Lee (NCT)
Brian Kang / Young K (DAY6)
Choi Wookshik

Australian 오스트레이리아/ New Zealand 뉴지런드: Speak English, has an Aussie/Kiwi accent, used to Aussie/Kiwi culture.
Jennie Kim (NZ)
Rose (Aussie)
Kevin Kim (ZEA; Aussie)
Lily M. (Aussie; JYP trainee)

Japanese일본: Very similar to Korean culture, may speak Japanese fluently, used to Japanese mannerisms, used to anime, cute things, the exotic fashions.
Kwon Rise (RIP)

Other: Filipinos are used to their Pinoy culture, may speak Tagalog and English; British will have an accent with English, used to English culture, proper, has different slang than America;
Sandara & Thunder Park (Filipino)
Seo Herin (fmr SM Rookies, Idol School)
Son Sungah (Fiji)
Yang Jiyul (fmr Dal Shabet; English)
Lee Seul / Jessica Dew (Idol School, fmr High Teen trainee; not an idol anymore)
Clara Lee (Switzerland)



 

Remember:

English is spoken throughout the world. Accents occur in every culture/country. The UK & Ireland have very diverse accents and not just an English accent. Americans can carry Cali, Southern, New Jersy, New York, and other accents. Canadians have an accent. Koreans learning English may have an accented intonation since they are native in Korean; they may learn from various teachers and retain their accents.

Mannerisms are a big thing. A lot of foreigners have to learn Korean mannerisms and respect their culture. Foreigners (위국인 way-gook-in) are called out, noticed. Americans are preferred (I heard this from various Korean sources).
Some mannerisms include: (but aren't all)

+ Bowing, depending on level of respect and age, the bows can be small (head bow) to very form (90 degree bow).
+ Shaking hands. If you shake hands, put your opposite hand under your arm/elbow. It's respectful.
+ Asking age (year born) and all that personal info is necessary and polite. Even if you aren't used to it.
+ -씨 (formal, sshi) 님 (nim, very formal, usually teacher or higher up)
+ Calling full name. But, of course, in Korean. (ex 손소희! Son Sohee!)
+ Taking off shoes at door.
+ Waiting for elders / those older to eat before you do. Unless they request you eat first.
+ When drinking, turn your head slightly and cover your glass; this is if you're with a higher up person (i.e. president of company, manager, older friend, boss, etc.)
+ Paying for others. If you are told to pay, you pay the whole bill. Next time, someone else will pay. Probably.
+ Only call older friends 언니 Unnie and 오빠 Oppa when you are friendly. Most fans do this, and it's okay, but in Korea, it's used for friendships.
+ Always be formal until you are friendly. 반말 Banmal (informal speech) is disrespectful if the person is older than you.
+ You eat from the same plates, grill, bowl, etc.
+ Keep drinking if an elder requests so.
+ Saying "왔어" as 'welcome, you're here, etc.' is common and a greeting.
+ Going to bathhouses together. Washing together. Changing together.



For me, being American, here's what would happen in my case.
As I grew up in Southern America, I'm pretty darn formal with people and very respectful, so learning respectful behavior is already there and not hard to adapt to. I'm also an open-book, so being friendly, helpful, and sharing is in my nature. I am also way too generous and I'd probably get taken advantage of. Plus, we already take our shoes off at the entryway, so I'm used to that. In my case, I don't think it'd be hard to adapt, but to someone very independent and anti-social and a bit rebellious... they may find it difficult.
if you have anything to add, comment.

Example from Tumblr:

"As someone with multiple bilingual friends where English is not the first language, may I present to you a list of actual incidents I have witnessed:

• Forgot a word in Spanish, while speaking Spanish to me, but remembered it in English. Became weirdly quiet as they seemed to lost their entire sense of identity.
• Used a literal translation of a Russian idiomatic expression while speaking English. He acually does this quite regularly, because he somehow genuinely forgets which idioms belong to which language. It usually takes a minute of everyone staring at him in confused silence before he says, "Ah...that must be a Russian one then..."
• Had to count backwards for something. Could not count backwards in English. Counted backwards in french under her breath until she got to the number she needed, and then translated it into English.
• Meant to inform her (French) parents that bread in America is baked with a lot of preservatives. Her brain was still halfway in English Mode so she used the word "preservatifes." Ended up shocking her parents with the knowledge that apparently, bread in America is full of condoms.
• Defined a slang term for me... with another slang term. In the same language. Which I do not speak.
• Said an expression in English but with Spanish grammar, which turned "How stressful!" into "What stressing!"
  
  
   

For me, learning Korean (or any language) I immerse myself in the language with everyday things. I have my computer and phone changed to Korean, I watch Korean shows, and keep learning Korean. Therefore, sometimes, I forget English words.
Example 1: Singing "Happy Birthday" in English and I forgot the lyrics.
Example 2: Trying to translate some Korean phrases into English but they sound weirder in English and I confuse my family.
Example 3: 헐 진짜 그래 그럼 알아요 아니 없어 싫어 어 왜 - better in Korean than English, therefore I struggle to equivalate them.