The main language spoken in Prague is Czech, although English is fairly common in the shops and restaurants I've visited. One thing I've learned is that you don't always need to speak the same language to understand each other. Many shopkeepers know enough English to help, and when we get stuck, a little hand gesturing and patience usually get us through the conversation. Shopping for groceries is a different story! Most packaging and labels are written in Czech, so my phone's translator has become one of my best friends.
I've found that reading Czech is much easier for me than understanding it when spoken. Czech spelling follows fairly consistent rules, and some written words look familiar enough that I can work out their meanings. But when people start speaking quickly, keeping up is another challenge!
What I've appreciated most is that when I make an effort to speak Czech, people often seem to appreciate it. Even if neither of us speaks the other's language perfectly, we're usually able to meet somewhere in the middle.