This is an anecdote of 1, but I grew up in France speaking French and moved to the US at 11. I don't have an accent when I speak English or French. I'm truly bilingual. I feel like I have way less anxiety, am more relaxed and have more confidence when I speak French, and it's not just the setting. I've done it for long periods of time professionally, on dates, etc.. I don't know if there's anything to this. To me it's always felt like there was.