Well I speak my native German and have always excessively used English due to a personal love affair with the language, and besides that I can order drinks in French and Italian. But here’s the Italian METATRON who developed his own technique to learn to speak 10 languages. And it’s a very effortless and logical technique.
Throughout his day, he speaks the languages he wants to learn, naming what he does; e.g. “I’m brushing my teeth” in the target language right before brushing his teeth and so on. Naming what he eats during breakfast or dinner – and as you eat different things all the time, over time you’ll learn all those terms.
In my opinion this technique works because your brain associates things you learn with places where you’re at – a technique known from Monks learning religious books by heart while walking through their monastery, associating terms with places subconsciously.