While I've been living in Czech Republic, I've been to dozens of interviews, and I wanted to tell you how language is actually tested when it's needed for work.
For those not in the know - I currently work in Azure tech support at Microsoft, and in tech support language is your main instrument. I know that traditionally in RuNet it's customary to shit yourself when English is tested at an interview, so I must share my experience.
The most popular way to test language - you come to an interview, and you're immediately asked what language you're comfortable speaking. Here it's important not to mess up and not say something like "only Russian", because there's a trick in the question - if English and Czech are needed, it means you're comfortable speaking exactly in them.
Secondly, usually at Czech interviews it happened like this for me - the interview starts in Czech, goes for about 10 minutes, and then the HR girl gets the idea to talk to you for 5 minutes in English. Here it's important to just speak confidently and not overdo it - usually the HR girl herself finds it hard to speak in English for more than 5 minutes, so if you're a genius in English but a dummy in Czech, don't insist on continuing in English.
If you're interviewing in Czech Republic at a small company, it will be a plus to show that you'll understand colleagues - joke about something basically. Not important, but a plus.
If you're interviewing at a corporation, you need to mentally prepare for the fact that they have language tests that just need to be passed, for a checkmark. Therefore, for example, I wasn't outraged that at Microsoft future colleagues called me to check my Russian and Spanish (yes, even Russian, despite the fact that I probably know it). The check was by phone, i.e. they checked precisely conversational abilities. But at a Facebook interview it was a complete circus - they called me and said that within 15 minutes I need to write an essay in Russian of 100 words, photograph it and send it to the interviewer. This is done so you don't call your smart friend to talk for you.
There are, of course, fun cases where they jerk you around for an hour and then don't even call back, but these firms don't interest us.
In general, I just want to say - don't be afraid if someone decides to check your language at an interview. Under the hood such tests are simply a desire to make sure you can find common ground with a person. In the end, you'll be judged not by linguists, but by ordinary people who already work there and know what level of language is required, i.e. essentially, you just need to not drop much below the interviewer's level.
Another thing important to understand - language will never be the deciding factor for hiring you, but it's a factor that opens the very first door at an interview, through which, in my experience, already 80% of applicants don't pass.
Well, since you're already reading my article in Russian, remember that if a person speaks Russian, English, Czech and Spanish combined, it's highly likely that they're not English, not Czech and not Spanish, so don't forget about your advantage and use it wisely.