When you live overseas, there are more things you need to become bilingual in besides actual languages. In my everyday life here, I am constantly switching back and forth between my native "language" and second "language" of the following areas.
Shoe and clothing sizes. Yes, there's small, medium, and large, but there's also UK, US, and Euro. They are all different. Over time, I've become fluent in my own sizes, but it is almost beyond me to keep up with the kids' sizes, especially in shoes. Some clothing stores (like H&M) list all the sizes on the inner tag. I treat this as my dictionary.
Currency. We've lived here long enough that I consider myself truly bilingual in both dollars and dirhams. For most things, I don't have to convert at all. In fact, at the grocery store in the US, every once in a while I have to convert the dollars to dirhams because that's what I'm used to seeing at the weekly shopping trip.
Temperature. Jeremy and the kids and I routinely discuss temperature in Celsius. But I get a little foggy around the colder temperatures because we never have those there.
Distance. I learned kilometers at an early age, thanks to running track and cross-country in high school (we were on the 1500m, 3000m, and 5000m system there). So it's been easy to pick up kilometers/meters/etc. here. (The metric system is better, y'all. Just sayin'.)
Islamic calendar. It is really helpful to be able to know when Ramadan will be next year, or which week you're going to get off for Eid al-Adha. If you speak Islamic calendar, you can do this in your head (shift everything earlier about 10 days a year).
Time zones. The US-based credit card customer service center is only open M-F, 8a-5p, EST. Quick, what are your available windows of time for reaching them from the UAE? Don't forget to carry the one/account for the Friday/Saturday weekend in the UAE vs. the Saturday/Sunday weekend in the US. I have to hack this stuff out practically with pen and paper every time. Except for half the year when Oregon is 12h behind us. That makes it niiiice and easy.
I know I said these aren't actual languages, but sometimes they are. You also have to be bilingual in every English accent there is. And some of them are pretty tough to wade through. Sometimes you smile and nod...and then smile and nod some more.