Almost all of us have had one concern when embarking, will they speak our language? Can I make myself understood? What language will the excursions be in? Anyway, these and more questions I am going to try to solve for you in general, but I recommend that you always ask the travel agency with which you are booking your cruise.
The first thing is to accept what our ability to handle in another language is, including in this English which is like the most international.
Continuing with this idea of know what our own possibilities are to handle ourselves in English, language that I take as a reference, I tell you that If you have a high level of this language, you can choose any shipping company and any port of departure without problems. The port of departure is important, because most of the passengers who board the cruise will be of this nationality.
If you defend yourself, but you cannot follow a conversation I would tell you that on a first cruise you choose a European shipping company such as MSC, Costa or some Royal Caribbean route that leaves Spanish port. If you see that in the brochure or where you have booked the trip it says: Mediterranean details, it means that they have a minimum of attention in your language.
If you find it difficult to speak English, I recommend you travel in Pullmantur, at least until you have learned the dynamics of how cruises work, it is not very complicated, you will get right away with it.
And well, I also tell you, in every shipping company in the world there is someone who speaks Spanish. If you travel in the Premium category, you can request that the butler assigned to you do so, but because you feel more independent and secure, I have recommended these options regarding languages ... And then there are the Tablet and smartphone applications that translate everything and they open doors for you anywhere.
So I wish you a happy journey and happy learning, because surely knowing a lot or a little will always have the opportunity to practice other languages on board.