When you learn a language, you actively change the shape of your brain by creating new pathways.
You practise rote learning and are constantly memorising new words, you use new grammatical tools, you flex your brain in different directions to adapt to a new logical system and you're constantly making choices (one word over another, one tense over another, etc.). Not to mention the fact that you're adapting to cultural differences!
That learning a language impacts our behaviour therefore seems logical to me. Even more so that it helps with decision-making, as explained in this fascinating article from The Guardian.
As I always tell my students, confidence comes from speaking and realising, as you speak, that what you chose to say is understood by your interlocutor.
You don't need external confirmation, nor validation, because you keep on communicating ! The proof is literally in the pudding and that is why language learning is empowering.
Don't hesitate to send me your questions.