I'm Indigenous Canadian and I grew up in a semi remote community where my family only spoke our Ojibway/Cree language. That was my first language for about the first ten years of my life.

I went to school and learned English and could understand it from a young age but I never needed to speak it.

At 14 I had to go high school in a city where everyone spoke English and I didn't. I could understand everyone but I had a hell of a hard time speaking or even to be heard. My brain knew what to say but my mouth parts were so out of practice that I couldn't speak properly or be understood. The software was working 100% but the hardware didn't cooperate.

I had a hard time speaking English all through my teen years. I didn't get comfortable with it until about 20. Even after that I spent about another five / ten years before I got fully comfortable with the language. I'm almost 50 now and I can comfortably speak English now and I have no problem making myself heard. Sad part is that in all that time, I've lost some of my ability to speak my Indigenous language.

Basically it's just practice and sticking with it. You won't sound right or you won't sound good for a few years but keep at it. Make mistakes, make yourself sound goofy or silly ... who cares ... keep practicing and eventually you'll get better with it. It took me a long time because I just don't like interacting with people. I saw others like me who were more extroverted pick up the language a lot faster and within a year or two just become as normal of a speaker as anyone else.

Practise ... it's like saying you want to learn to sing ... you won't be good at it at first so you have to practice and not be afraid to fail and fail often ... keep at it and eventually you'll be just as good at speaking as anyone else.