The "Arduino language" is C (with some C++ classes thrown in). On top of C, there are some predefined functions that handle common tasks like reading pins, writing to pins, generating PWM waveforms, etc. But they're not a separate language, just pre-written functions that you call from C. You could program it directly in C (or C++).
The Arduino is a good way to become familiar with microcontroller programming in general. It is not as intimidating as a more powerful starter kit like the one you mention and would probably serve as a good first step. If/when you are ready to work with a more powerful kit your knowledge will transfer.
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