Installing fonts in Debian is really easy nowadays. But, even so, there seems to be a wealth of outdated information on the Internet. So I'll be providing my easy way, for others and myself in case I need this information again. The first thing you need to do is downloading the fonts and putting them into one of the optional directories. This could be .fonts directory (notice the plural) in your home folder or a system wide folder such as /usr/share/fonts . In my case, I created a folder in /usr/share/fonts/truetype/ to keep my own fonts that I downloaded and installed. After putting the .ttf files into this directory, you will have to clear the font information cache files so that the new fonts are picked up and ready to use with applications such as gimp, openoffice etc. The command to be used is:

# fc-cache -fv

After this, you should be good to go. By the way, if you are looking for fonts including Turkish characters, fonttr seems to be a good place to go.