AFAIN you can use only latinic alphabet in your name.
"Incorrect name. Probably too long or too short" - name should be more than 3 symbols, starting not with a number (or even not with some special symbols).
Also it could be connected to your keyboard layout.
I'll try to explain process step by step.
1. Open your game folder
2. Run Updater.exe just in case (won't solve anything)
3. Run FOconfig.exe
Change port to 4001. And
press save.
4. Press play (or start the game any other way).
5. Press Registration.
6.
Press into the field where number 1 located at the image. It will open up with name and password fields. Write down name: kkknnn and password: qwerty. Add 1 number to end of name if needed.
Boost strength to 10, tag Small Guns, First Aid, Doctor (it's just for the sake of testing).
7. Press Blue Checkbox between number 3 panel and number 5 panel.
8. If it doesn't work, remember the mistake, press registration again.
9. Copy (ctrl-c) past (ctrl-v) any one of these names: kkknnn, kkknnn1, kkknnn2, kkknnn3, kkknnn4, nnnkkk1, nnnkkk2, nnnkkk3, nnnkkk4 to the name field.
10. Press Blue Checkbox.
8. If it doesn't work, remember the mistake, come back and tell us it.
Don't use those names and password for your own character, its all just for the testing.