I don't have one "stock" project that I always use for learning new languages... I just do whatever I happen to be thinking about at the time. Long ago, that meant an AD&D (2nd Ed) character generator. Then it was a training database for the volunteer fire department I was with. Later it was an (aborted) attempt to build a decentralized /federated social-network (something like Diaspora, IOW).
When I started learning Groovy and Grails I just started building a Reddit-like app that would become the first project of what would become Fogbeam Labs.
Now, I'm working on learning to use Angular, so I've decided to start on a product management dashboard thing I wanted to build for internal use here at Fogbeam.
So, advice? Just pick something. You say you don't have an "itch to scratch", well OK... if you don't have something new you want to create, just pick an existing $WHATEVER and port it to your chosen language. Pick something you use regularly so you'll know and understand the domain, and start coding.
It doesn't really matter if you finish it or not, or how good it is. The goal, remember, is to learn the $NEWLANGUAGE not to build a better $WHATEVER. But who knows, maybe the $WHATEVER project will turn out great, and you can wind up actually using it or making a business around it. But if not, it still served it's purpose.