ibus-bogo is a Vietnamese input engine targeting IBus, an input method manager in GNU/Linux environments created by a group of talented Vietnamese developers. You can install it in Ubuntu by the following command:
$ sudo apt-get install ibus-bogo
Its github repo: https://github.com/BoGoEngine/ibus-bogo-python
It works really well in the current release of xUbuntu (13.10, 14.04) in comparison with ibus-unikey which is buggy. But, there are still some annoying issues with ibus-bogo. One of them is Vietnamese input in Skype. The official documentations of ibus-bogo instructs us how to solve this problem by adding these lines to ~/.profile:
Log out and log in again. Then, restart the ibus-daemon:
$ ibus-daemon -xdr
Notes: In Xubuntu 14.04, I have to do this every time the system startup/reboot or turn off / turn on Skype.