- Boot PC from Live CD (Linux mint 18.3 KDE)
- Run in console:
sudo ecryptfs-manager
and exit (select 4 => Enter) (see bug 455709 mount: mount(2) failed: No such file or directory
)

- Find your encrypted
/home/UserName
directory by checking every device in Dolphin. In my case, it is located on a separate volume (But in your case, most likely this path will be inside the home
folder like: /media/mint/1234567-1233-1233-32423-1a95b2c5dc68/home/UserName
)

- Open dolphin in home directory "as root"

- Press
Alt + .
for show hidden files

Go to .ecryptfs
folder inside and try to find .Private
folder (in every new Folder you have to "Show hidden files" by pressing Alt + .
!!!)
As final your .Private
folder:

- Press
F4
for opening console here
- Run in console:
ecryptfs-recover-private ./.Private
(Passphrase is your login PC Password !!! )

- Well done! Go to
/tmp/ecryptfs.JSiaYsbz
directory using cd

p.s. Use the flag --rw
(in step 9) to mount the encrypted filesystem as read and write (read only as default!)