A little about me (though it would be cool if responses have broad applicability for others in a similar position):
Although my research interests are predominantly Europe-based, I only speak English, and I cannot bring myself to, for instance, move to Germany and intensively study German knowing that I may realise at the end of it that I want to study French history instead...
Thanks, and again please remove if inappropriate
First things first: if you want to do a PhD in European history, you will almost certainly have to learn to read two languages besides English simply as a program requirement (at least, this is true in the US). That doesn't mean you have to move to Europe! Pick up a copy of Sandberg's French for Reading and get on making those flashcards to go with the exercises.
Secondly, the only way to figure out what you love is to know what's out there. That means read. A lot.
If you've not narrowed down your interests beyond "modern Euro" and you have only English, it's probably a much better bet to go about this with some structure--that is, look into master's degree programs. You'll take some classes, explore some different topics, hone in on whether your internal fire is stoked by the impact of "muscular Christianity" on English girlhood and the impact of English girls on muscular Christianity, or by British intelligence operatives in Northern Ireland during the Troubles, or wanting to revisit Marxist perspectives on the English Civil War, &c &c. A master's degree will also give you the opportunity to see whether grad school and its prospects is the right decision overall for you.
If you're in Australia and you end up doing your PhD here, then technically you don't have to learn any languages as a program requirement. Australian PhDs rather assume that you will have, or will develop, any language skills you need. That can work to your favour, or not. If your interest is European history you can't avoid learning languages and you shouldn't be trying to (would you trust an historian of French history who couldn't read French?)
But, as with /u/sunagainstgold you do need to figure out a research area to start pursuing. And the way to do that is to keep reading and researching, informally or formally, until you find something that's going to be interesting enough to (a) generate a PhD worth writing, (b) is going to grip you enough to get through a PhD (though mere "interest" doesn't sustain you through one, you will need to bring some grit to the table).
Hmm, not sure I have anything else for you atm, but happy to think on it a bit.
source: am an Australian with a PhD in ancient history.