What is the best language to learn when visiting eastern europe?

Speak in English!!

Allow me to correct you as the countries you've mentioned are NOT in one region at all. The languages spoken are so dramatically different that you will be unable to communicate if you have knowledge only on one of them to the rest. Most of the people speak (especially the younger generation) English, then as popularity comes German and French.

FYI:

Czech and Slovenian are Slavic languages

Hungrian is a Finno-Ugric language

Romanian is a Romance language

so you chose language from three different groups...

I would suggest English as the first language... and if you want to use a Slavic language, I'm pretty sure that there's a significant number of people in Central/Eastern/Southeastern Europe who still can speak at least some Russian...

I am pretty sure that German is understood throughout the region as well...

I wouldn't expect too many people speaking Spanish or French in this region (possible French could be understood in Romania since French is in the same language group as Romanian)

Hope this helps...

Where exactly in Europe are you planning to go? If you are visiting for 2 or 3 weeks rather learn some French - it is a bit easier. German is difficult and to be understood you have to have good working knowledge of the grammar. If you are travelling in western Germany almost all people will automatically switch to English no matter how good or bad you speak German - happens to me often and I am fluent.

Hungarian is unlike any other language, distantly related to Finnish; Romanian is a Latin-based language; in Czech, you may be able to get by with some German; Russian may help you in most of those countries, however, many peole there frown upon using the language of their former occupiers.

English, French and German are fairly universally spoken on the continent.

Have fun!

English

English will get you everywhere. You have no time to learn another language well enought to put it to good use. Just bring a few pocket dictionaries (English-German, English-Romanian, etc.) People in Eastern Europe are always happy to show off and use their English, so let them have this opportunity. And have a good trip!

Esperanto, for a couple of reasons.

First, there are relatively a lot of Esperanto speakers in that area. You won't be able to stop a random person on the street and talk to them in Esperanto, but then again there's no other language you will be able to use to talk to most people you sotp in the street. (A different language is spoken in each of those countries.) However, you will be able to make contacts with local Esperanto speakers wherever you go, and get to know locals and the local culture in ways that most travelers/tourists don't have available.

Second, you have a reasonable chance of getting to know Esperanto to a good degree before your trip. National languages are hard, and unless your trip is in a couple of years and you dedicate a significant amount of time every day to studying, you'll barely beyond the stage of stuttering and gesturing while you hunt through your pocket dictionary to find the right word. Esperanto takes a fraction of the time to get to know to a reasonable degree, so you can spend your trip talking to people and getting to know them, rather than feeling like you have a speech impediment like aphasia.

woo im originally from there!

the majority of people there speak English. Try learning french if you don't already know it.

other than that, all those countries speak very different languages.

have fun on your trip!

german is spoken quite popular in czech rep. and russian is widely used throughout, but romanian is quite different from, the rest, i wouldn't struggle to go and learn czech, slovenian or hungarian, because they are incredibly difficult, expecially hungarian!

here is a few romanian, czech, and russian phrases for you

hello

cz- ahoj

ro- bunã ziua

ru- privit

goodbye

cz- na shledanou

ro- la revedere

ru- proshania

thank you

cz- dekuji

ro- gratie

ru- spasiba

have a good trip