Most Qatari's can speak English or at least speak English at a basic level. If you want to be safe, or even want to learn a new language, here are a few important phrases!
It should be mentioned that different Arabic countries have different accents. In addition to that, there are TWO forms of Arabic. Traditional (which is used when writing always and sometimes when spoken) and then you have the casual dialect (which is commonly used for speaking).
Arabic is also a bit tricky because some words change depending if you are speaking to a man or a woman. It is similar to French which has Masculine and Feminine words.
The words I have given are common Qatari used words (understood in 90% of Arabic countries)
It is also important to know that even if you mispronounce a word and don't say it correctly, arabic people can usually guess what you are trying to say.