Thanks for my leadership.

All of a sudden (you could also say All of a  suddenly) I would like to borrow take the opportunity to write a small essay to thank my leadership (leadership would be a team of leaders, or if you said i would like to thank my boss for his leadership. or you could say i want to thank my boss). Even though I have never personally told him that he would never see, this is also quite good~. ("never see, this is also quite good"  is a bit confusing, try and say it another way so i can correct,  what would he never see? what is quite good?)
The company I work for is in good order and business is stability stable，so everyone is happy. My leader is very friendly and never loses his temper. Basically do not work overtime (you could say he does not ask me or make me work overtime) and not too much work pressure (it would be better to say "he does not pressure me too much at work"). So that I have enough time and energy in my spare time to do what I like and what I am interested in. Such as take an interesting course. For example, after the completion of the work (it would sound better to simply say "after work"). I can spare time to write a small essay.hah~
My life is not just work, I can focus on more interesting things.
I think it's that is  lucky.

Thanks for my leadership boss.

All of a sudden I would like to take the opportunity to write a small essay to thank my boss.Even though I have never personally told him that he would never see, this is also quite good~.(This sentence doesn't quite make sense. I think you mean that you have never thanked your boss directly before, and you don't want to? You are only writing the letter for yourself, not because you want to really thank your boss)
The company I work for is in good order and business stability (this is a little bit weird. Maybe you could say, "The company I work for is in good order and its business is stable") ，so everyone is happy. My leader is very friendly and never loses his temper. Basically I do not work overtime and do not have too much work pressure at work.So that (It would be better to say, "Because of this,") I have enough time and energy in my spare time to do what I like and what I am interested in, such as take an interesting course. For another example, after I finish work, I have enough spare time to write a small essay. hah~
My life is not just work, I can focus on more interesting things.
I think this is lucky.

Nice job! It's great to have a job that gives you flexibility outside of work.