I disagree with Josep and Oscar. They are looking at this question from the point of view of being Catalan speakers, not as a student of Catalan (or other Latin-derived languages). Relatively speaking, as with all Latin-derived languages, Spanish and Catalan are similar, and this is especially so if you come to this question from a Polish perspective (or if you've studied Asian languages, for example). Like Oscar says, Spanish and Catalan are as similar as, say, Spanish and French, or Spanish and Portuguese, or Italian and French. Does this mean it's easy to learn both Spanish and Catalan at the same time? Not necessarily. I find Catalan quite hard to speak and write, but because I can speak French and Spanish I understand Catalan very well. It really depends on your linguistic background.

It's not impossible. It doesn't make learning difficult, on the contrary, it makes it more interesting, and quite funny. Good Luck!

no. they are not as similar as you may think. and maybe after you will rethink about the beauty of languages (at least at phonetical level, but i dont care much about this). Wanna an example? ok...here one: 1. No hablo español con nadie porque casi no me acuerdo de nada. 2. No parlo catala amb ningu perque gairebe no me'n recordo de res. español/catala interchangable. phrase meaning irrelevant here!

I agree with Josep. Beyond some very basic things they're not that similar. Or they're similar like Spanish and Portugeese. Or Spanish and French. You might understand Catalan with some practice without really learning it. But you'll get stuck when you want to speak it or write it. You're likely to end up speaking a mixture of Spanish and Catalan when you want to speak Catalan, it's called "catañol" (català+español). (This is not official by the way, just a funny way of calling bad Catalan). I know what you're thinking, one will be like a nice bonus for the other. MAYBE. But maybe it'll be just as time consuming as learning two entirely different languages. None of my American friends (who speak very good Spanish) understand Catalan. I would say the best thing you can do is to try and get some first hand experience to make your own opinion. Good luck.

this isn't a mission impossible, we can do everything that we propose to do as a goal so ! go ahead ¡