Ah, that seems to fit it with what a lot of people have been saying. If you grow up speaking both languages it's very different than if you learn one later-or perhaps it's more accurate to say if you start speaking one later. That is, you might learn a language from an early age in school, but only use it regularly when you move to a different country when you're older.

For example, I may speak English most of the time, but I find myself inserting Chinese, Malay, or dialects in instances where they will make my point (in the conversation) more succinct.

That does make sense--and also fits with the idea that growing up as bilingual is a different experience that learning one language and then another, or having the languages separated into what you speak in one place or another. I love the idea of creating a third language that mixes the two together. It's both more personal (since each individual might have a different preference for what expressions they like in each language) and a standard language (because I'm sure some expressions naturally get used by everyone).