In order to install MS True Type fonts in Ubuntu you have to install the
sudo apt-get install ttf-mscorefonts-installer
After installing the package regenerate the font cache:
sudo fc-cache -fv
Now you can use a bunch of MS True Type fonts in Ubuntu.
Segoe UI font, however, is not part of the
ttf-mscorerfonts package, so you have to search and get a
segoe-ui.ttf for yourself. (either by extracting it from a windows ISO or installation or by searching through the internet, i guess it should not be too hard to find one...)
When you have our
segoe-ui.ttf file, copy it in a foldr called
~/.fonts. If no such folder exists, create it, no problem.
Now again regenerate the font cache:
sudo fc-cache -fv, and voilá. Now you are able to use
Segoe UI font on ubuntu.