As answered in Getting a syntax error when I type pthon on Ubuntu 18.04, the issue is likely due to one application (exaile here) expecting python 2, and you having python 3 as the default.
In particular, check sys.path. It likely points to python 3.5, i.e., it includes /usr/lib/python3.5/site.py.
As per official documentation, sys.path is a list built from PYTHONPATH and other installation-dependent paths.
As a quick check, find if you have any python 2 in your system ($ python2 --version).
If so, find where is the corresponding site.py located, most likely /usr/lib/python2.7/site.py.
Then,
$ export PYTHONPATH=/usr/lib/python2.7/site.py
$ exaile
If this works, then for a definitive setup you would have to find a way to change your sys.path when executing exaile.
There are quite a few options, depending if you launch it via command line or a launcher. For instance, you could write a script that exports with export PYTHONPATH="/usr/lib/python2.7/site.py:${PATH}" and then executes whatever you need. That can also be the target of your launcher.
PS: Note also the best way to add to PYTHONPATH
