As tUt says, you should have no problem with the language... I always use the term Vienna and I am always understood, but the Slovak or the Austrian will all do...
2 Points to note. If you go to Hlavna Stanica, make sure you follow tUt's advice and go to the counter nearest the platform (you have to go up 3 or 4 small steps)... the first ones you see are for domestic tickets only.
Second, the 10.34 train leaves from Bratislava Petrzalka station - make sure you go to the correct station!
Also, the counters have a sign which states that you must tell them you'll use a credit card before you ask for your ticket - I always follow this advice, because you never know...