Pig-Latin but very fast. Decades of practice.

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 🥰

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.

Nice try.

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

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.

English.

When we travel: speak japanese. Else, we've been together enough to know each other pretty well and often don't need to say much aloud to communicate something

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

We have a code for when we're ready to leave a party. One of us will go to the other and do the finger walking up the other's arm. This means "I want to go home."

My AuDHD self went and married another ADHD person, and we are both full of little non-verbal cues we give each other, and they range from Significant Glances to discreet groping. We communicate well (and I 100% think the reason we get along so well is because we communicate) and non-verbal is just part of it.