His Arduino callout limits the available practical options greatly. In his situation minus Arduino, I'd go with Go. It works really well on ARM devices like the Raspberry Pi and all the way up to Windows/Linux/Mac x64.

Go is my current first-choice language if I have the choice. Of course, in today's very segmented platform (web, desktop Windows, desktop Mac, desktop Linux, Android, iOS, WinPhone, et al) era, there's really no one language for everything. Even C falls down in some areas.