Practice makes perfect

It sucks to be a beginner.   Or   Being a beginner sucks.   [And not rude... you wouldn't say it in front of the Queen of England, or your bosses' boss, but we use this phrase a lot among family and friends. If someone were to tell me their family member died, I'd say as my initial reaction, "That sucks."  It means: "How awful!  Such a pain. What a terrible situation". ].

Sucks is a word that can be a bit grosser in conversation, too, if expressed differently. "Go suck a d---" is an insult often said between rude men, but this form needs a direct object and there's other words that demonstrate the sexual nature of this. But also, kids suck a lollipop or suck on a pacifier and this is innocent in meaning.

If you say "He sucks" about someone, it means that your boss is a jerk. "He's terrible..." is the meaning. "This sucks" means your current situation isn't bringing you joy.

When you start learning something, it's normal to see professional people doing the same thing you want to do and think that you will never be like them.  Perfect!

It happened to me when I started learning English, I couldn't understand anything in English and having a conversation with a native speaker was an impossible thing. At the same time I used to watch polyglots on YouTube and I thought I would never be as good as them.  Polyglot is a noun describing people, so you don't need another noun, like "actress people" is written "actresses".

I'm not there yet, but I've practiced a lot and now I can understand most of what I read, and I can talk to natives if they speak slow. I guess that idiom (practice makes perfect) is true, although I still need to practice.

Other options for "I'm not yet." : I'm not a polyglot yet.   I haven't arrived yet. 

there means "I am not in that place in the future yet."  Like I want to be a celebrity, but I'm not there yet. She's worried about what life will be like in her seventies, but she's not there yet."

Practice makes perfect

It's a common slang term. It's not that rude, but don't use it at a, say, formal event.

When you start learning something, it's normal to see professional people doing the same thing you want to do and think that you will never be like them.

It happened to me when I started learning English. I couldn't understand anything in English and having a conversation with a native speaker was an impossible thing. At the same time, I used to watch polyglots people on YouTube and I thought I would never be as good as them.

I'm not yet, but I've practiced a lot and now I can understand most of what I read and I can talk to natives if they speak slowly. I guess that idiom, "practice makes perfect" is true, although I still need to practice.

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I know what you mean. Sometimes it helps a little to put a positive spin on it. Like, instead of "I wish I could be that good", change it to "One day, I'll be that good if I keep at it".