Did Voldemort ever plan to extend his rule to the other wizarding societies outside of Great Britain and then eventually topple the International Statue of Secrecy and take over the Muggle world as well?
You can surmise that he had to start somewhere. His greater plans are never revealed but, as with all slaves to power and ambition you can imagine that overall world (universal?) domination would have followed UK domination.
I imagine that, once Harry was dead then nothing would stand between him and UK domination. Replace the ministry of magic with his own mechanisms and then influence and/or conquer the 'other' ministries (I'm assuming that France, Romania, etc.) have their own magical 'governments'.
Can you imagine Voldemort conquering hogwarts and then sitting down with a cup of tea and saying 'time to retire' ?
However, according to the books his main desire was for the post of 'defence against the dark arts' at hogwarts and then, we can speculate, headmaster. But, as stated before, he'd need to broaden his horizons far beyond that . . .