ESL installation
ESL is not installed by default. You must explicitly install it from packages, or compile and install it from source.
If you're installing from Debian packages, then you want to install libesl-perl, python-esl, freeswitch-mod-perl, freeswitch-mod-python, and so on.
If you're compiling from sources, then you want to check on out http://freeswitch.org/confluence and search for "Event Socket Library" for latest dependencies and installation instructions.