How to restore default Ubuntu environment?

Question

linux

Good day!
In general, the essence of the problem:
Somehow in my spare time it seemed to me that my ubunta looks ugly, I installed Gnome 3.
In the gnome I observe the problem of changing the keyboard layout - the layout does not change the first time, sometimes not the second. And I don't really like the design of the gnome.
Maybe I deleted something, now Unity won't start.
Question 1: How do I get back the default environment?
Question 2: is it possible to somehow solve the problem of switching keyboard layouts? Googling, I found several ways that did not help me.
Thank you!

Answer 1

If you need exactly unity, then
If KDE, then it was advised above
sudo apt-get install kde-full

Answer 2

sudo apt-get install kde-standard

Answer 3

If you want a beautiful system - install Linux Mint with Cinnamon
Well, or sneakers, also an option, although they are not very good for me