I'd like to get started writing a Scope for Ubuntu.
What programming languages are available and what should I choose?
Once upon a time, scopes had Python and Vala bindings. Python was the recommended language. This actually still applies for the desktop and Unity 7. However, while it will still be around for a bit (i.e. it's still shipped in Ubuntu 14.04 LTS), we're phasing out Unity 7 in favour of Unity 8 in the new world where we'll have a single Unity codebase that runs across devices and form factors (e.g. phone and desktop).
The reasons for going for C++ are twofold: performance and compatibility with the Qt APIs available throughout the platform.