This might or might not work, depending on the type of font you have. (TrueType, etc) If you have troubles, please comment and I’ll try to help you. ^_^
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1) Type or paste this command into Terminal: (this makes the directory where you store the fonts you wanna install)
mkdir /usr/share/fonts/truetype/fonts
2) Replace {fonts} with the names of the fonts you want to install, or you can just open up your file manager and copy and paste the files. Do the following in Terminal.
cp {fonts} /usr/share/fonts/truetype/fonts
3) Run this command to regenerate your computer’s font cache in Terminal.
fc-cache -f -v
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Have fun with your newly installed fonts!
[...] /home/username/ is basically the same as C:/Documents and Settings/username/ /usr/lib/ is basically the same as C:/Program Files/ /usr/share/fonts/ is like C:/WINDOWS/Fonts (There’s a nice guide on how to install fonts in Ubuntu here) [...]