The error you are getting is happening because your Vim doesn't include support for Python, which is required by UltiSnips, as that plug-in is implemented in Python for the most part.
My recommendation is that you should get a Vim binary from your distribution. You mentioned using Linux Mint, so make sure you are not using a
vim-tiny package, since that package is typically built with most features disabled. Instead, try
vim-nox which should be more featureful versions of Vim.
You also mentioned in the comments that
which vim points to
/usr/local/bin/vim, please note that this path is most likely not the one for a Vim installed by your distribution. Instead, your distribution's Vim will be in
/bin/vim (in modern distributions, these two last paths are typically the same, as
/bin is usually a symbolic link to
Not sure how you got a Vim under
/usr/local/bin/vim, did you happen to install Vim from source over there? Did you get a binary package from somewhere other than your distribution and unpacked it there? In any case, you might want to uninstall that one, to see if things start working back again.
If there's nothing other than Vim installed under
/usr/local (you can maybe find that with a
find /usr/local command to list all the files and subdirectories in there), you might be able to just remove that whole tree and recreate just the directories from scratch.
Another option is to change your
$PATH variable to list
/usr/bin ahead of
/usr/local/bin, for example
export PATH=/usr/bin:$PATH should do that for you. But that is just a workaround. The best option is to uninstall a Vim under
/usr/local that is clearly not working for you, and make sure the one you install from your Linux distribution is a fully featured and not a minimal build.