Korean

Pig-Latin but very fast. Decades of practice.

Sometimes Irish.

Around the kids, when they were young, we used French for those things we didn't want them to know about. She's fluent and I don't really speak it at all, but took it back in High School and remembered enough vocabulary to make it work.

Today, both our boys have taken years of Spanish and they speak in Spanish for those things that they don't want us to know. LOL

Around other adults, my wife and I have a system of looks that we give each other. We can have an entire conversation just by giving each other looks.

We have a Darmok and Jalad at Tenagra style system where we reference memorable past events.

Might just be cus we're both neurodivergent, but we have a lot of non verbal cues, though he's nowhere near as showy as I am.

Whenever I end up overstimmed and go non-verbal, I tug at his shirt gently, or paw at him. From then it's simple ASL. For him, he genuinely just has simple phrasing or wordings that are kind of "key words" between us. The both of us are high functioning in our 20s, this is just kind of how it ended up and we're both super not subtle about it. It's great.

Edit: we literally do pigeon noises at each other at random. One of us says coo and the other goes roo. It's literally just a "thing" between us and it started because of us watching pigeons together and it stuck.

Most people around us usually get it so isn't really a "secret" language, but my wife and I are big Simpsons fans so we talk in quotes all the time.

One that gets a lot of play is "I'm going... to... stalk... Lenny and Carl" for when we're going somewhere but really sure what we're going to do

Swiss-German is a pretty good secret language.

Perhaps more useful is to silently make your mouth into an "o" like you're saying "go" if you want to go, or a line like you're saying "stay" if you want to stay.

Ready to go home?

Steve is just a jackoff today. Right?

Yep. 😘 fuck him. Let's go home.

when one of us says something to someone else (usually our kids) that is going to screw both of us over the other says it "shut up, net face"

I handed my girlfriend a hair tie once while at my parents house. Good times were had.

English.

Very rudimentary Japanese, or incredibly elaborate/old Englishy stylized speech

I just text; don't have to worry about someone else picking it up.

My wife and I have a couple of terms that we frequently use.

• SET - "South Eastern Twat", used to describe a pretend-farmer, with gilet, flatcap and Landrover, who are so frequent in this part of England. We used to live in a more down-to-earth part of the country, so have allergic reaction to the stealth-wealth and snootiness you find down here.
• "There's no need for buttering the pan" - a description for ovulation days, when my wife gets quite randy :)
• ALTHAB - "At Least They've Had a Bath", which we use as a short-hand for "the kids had baths yesterday, won't need one today and therefore, if we push through, we can get them to bed early and might have some calm time together, in front of the TV, playing a boardgame or whatever is required to reconnect.
• HPS - "High Pressure Sex", a joke used to get us both to relax about those moments when you feel like you ought to have sex (you finally have a night away or whatever), but neither of you can be bothered (too tired, too stressed etc.).

This was taught to me,

Snuggle and cuddle. Tell the person you want to cuddle, means to curl up together under a blanket and watch a movie. Tell the person snuggle when you want to fuck (but your being discreet). And if your hair looks a little messed up or someone asks what y'all been doing... snuggling 🥰

Spanish

I wouldn't call either of these particularly secret, but whatever, they're fun.

Excess material = a very large shit, often multiple shits.

Trip insurance = using the bathroom before getting in the car, whether it's needed or not. I came up with this one as a child, and it's now in widespread use in my extended family, especially with the nieces and nephews.