If you're multilingual what language do you think in? Is it possible to switch if you acclimate to a new language?

I could have posted this in social but I’m looking for at least a few serious answers. I’m asking if you originally spoke say English but moved to mexico and started speaking Spanish all the time at what point do you grasp the Spanish without having to internally translate to English or is such a thing even possible?

What happens when you throw multiple languages into the mix? If a kid learns two languages at the same time in childhood which one do they think in to begin with?

If anyone is wondering I only speak English and barely that so this is a legitimate question for me…