Dear Curious Learner,
Don't worry! English (like any language) takes a long time to learn. First, you have to learn all the parts of a language: grammar, vocabulary, phrases, culture, etc. After that, you have to use learning strategies to help you put all those parts together. Listening comprehension, professional level writing, speaking like a native- those things all come with time and practice. Which brings us to our last point: practice! The more opportunities you have to practice, the more you learn. As I say to myself in my Spanish learning "¡Mis errores son mis profesores!" (My errors are my teachers!)
You may never speak like a native Californian or a Londoner; but, if you are able to communicate your thoughts, wants, or intentions and the other person understands you, you're speaking English well! Now, I know that you may think "That's not speaking fluently!" and you're correct, it's not. But how do you define 'speaking English'? For me, being able to talk to people about something I'm interested in or passionate about and having them understand me well enough to carry on a conversation is the goal.
We learn languages in order to communicate our thoughts to another person in a different way. Through learning a language we can start to broaden our understanding of how the world works. One of my favorite Spanish proverbs says: 'Cada cabeza es un mundo'. Meaning, 'Every head is a world', or as I like to think of it 'In every mind, there is a whole world'. Every culture has its own way of thinking about the world, just like every human sees things differently. It's completely acceptable for you to be very competent when speaking about Engineering, or cooking, or cars, or whatever you're interested in, while at the same time feeling like you can't say a word about the things you're not interested in. Just like in your own language, there are things you can't talk about. For example, never ask me about astrophysics. I'll probably drool on you. But, ask me about cooking, gardening, politics, or English language teaching and I'll bore you with my eloquence.
Learning English can be tough, but if you pick a topic you're interested in, the language learning will become interesting as well and the more likely you will be to want to practice. Trust yourself and if you don't understand something, simply ask 'Could you repeat that, please?"