How do I install glib?

You need libglib2.0-dev for glib-gettext. You can install it with

sudo apt-get install libglib2.0-dev

you also need to install libgtk2.0-dev in order to install glib completely (glib is a part of : libgtk2.0-dev)

sudo apt-get install libgtk2.0-dev

see this link for more explaination: installing gtk and glib

I recommend you search for available ppa's if you want to just checkout the newer empathy than you have. I think this ppa is the best bet Or just do this

sudo add-apt-repository ppa:telepathy/ppa

Or if you need to build it.

sudo apt-get build-dep empathy

which will install all the dependencies required to build empathy from source.