I'm at six natural languages now. I have worked in three of them and could immediately go to work in my field in a fourth. I could refresh the two others within weeks to a level where I could go to work in them, with some initial difficulties.

I would say that, to some extent, knowing several languages helps you with learning the next one. Not just if it has features that I already know from other languages, but also if it has new "WTF" aspects. Those become easier to accept.

What I mean is this. My last relocation was to France, for which I had to learn French. French has a bunch of things that make me go "WTF", but knowing that every language has such things makes it easier for me to shrug them off, accept that French is weird, and carry on. On the other hand, some other expats I know, who know fewer languages, question everything: Why does French do this or that? I have the feeling that some people get caught up in such issues and develop (or reinforce) an internal resistance to learning.

TLDR: Learning languages may make it easier to learn others by making you more accepting of weirdness.