It appears that recent paclet update interferes with
Shortcuts` package and breaks predictive interface features (autocompletion etc).
Before the issue is tracked down and fixed it may be required to uninstall it.
Needs @ "Shortcuts`"
and restart Mathematica. If that does not help one may need to delete
Yes, with a bit of effort it is possible to construct such a package.
My package Shortcuts, inspired by various questions and answers on this site over the years, can be installed in less than a minute from within a fresh notebook in Mathematica 9 or 10, on Windows, MacOSX or Linux by this
Note that during installation some dialogs will pop up, which I think should be always confirmed, though if you are very afraid of evaluating Dynamic content in notebooks from others, you might not want to confirm them (though then the shortcuts often trigger an "Enable Dynamics" question in notebooks saved in "insecure" locations).
All code is available on Github here.
I found Windows the most friendly operating system to add user keyboard shortcuts to.
Screen shots of the shortcut listings are:
The package Shortcuts` gets installed in $UserBaseDirectory/Applications and is loaded automatically when using a keyboard shortcut.
The package is documented in the Wolfram Documentation center.
If you want to get rid of the shortcuts just do:
which deletes the generated KeyEventTranslations.tr file $UserBaseDirectory.