I will learn java, c#, python and swift in udemy in 6months... purchase the courses, started , only did hello world for each course, never came back

Rather than thinking "I will learn language X" I'd suggest "I will make useful thing Q, it just so happens to be in language X" instead. I found this gave me a reason to go beyond hello world :)

@kkalem I can't agree more! But how do you find such idea ?
I mean, I have ideas, but so wide that I'm a bit afraid to start, and never finish the thing.. :/

Also, after doing dev all day, I'm not so excited to do more than 1-2 hours/day on personal devs.. :(

@Hakii The Q depends on what you can already do in a language(s) you know already. Maybe re-write an existing project if you got nothin. Comparing the results are often interesting as well :)