Yup, and this is especially true of languages that are completely different than your own. Immersion and osmosis are going to work a whole lot better if you're

Yup, and this is especially true of languages that are completely different than your own. Immersion and osmosis are going to work a whole lot better if you're going from French to Spanish, or English to German, etc. There's enough shared vocabulary and culture that it's easier to make assumptions about the intent of the speaker. That will not be the case if you're going from English to, say, Korean. Immersion is important for any language learning, but some prerequisite learning is needed to take advantage of it. I think those prerequisites stack up as you move further away from the foundation of your current languages.