Translation:Do you eat pork or chicken?
I think it's more that 还是 is here used to imply a question (see above/ tips + notes on the web version). I agree that the sentence is still slightly ambiguous. Can a native speaker give context/ clarification as to 'do you eat/ are you eating/ do you want to eat' using 还是?
还是 can be used as a kind of interrogative, listing 2 or more choices for the listener to choose. So in this question the choice is either 你吃猪肉 or 你吃鸡肉, and when we compile the options into one question, we leave out the second 你吃 to avoid being redundant. Thus adding 想 does not change this logic - you will still be offering 2 options, only the options now include the listener's will: 你想吃猪肉 or 你想吃鸡肉. So I said in a post above it is a bit rude not to say 想 because the options offered are not considering the listener's preference, but the 2 allowed outcomes only (it's like I don't have other food anyway, so are you eating pork or are you eating chicken?).
It's not a yes/no question. It assumes the answer is going to be either 猪肉 or 鸡肉. You can say 不吃, just as you can change the subject entirely, but that isn't what you're being asked for.
Imagine someone saying, "Are you going or not?" The intonation rises on "going" and falls on "not," and obviously they expect that exactly one of those is the case and that you're gonna tell them which.
Imagine someone saying, "Do you like the Beatles, or the Stones?" with the same intonation -- falling on "Stones." They expect you to like exactly one of those two bands. If you say the wrong one they're probably going to be rude to you. Or if you defy their expectation by saying "neither." Or if you say "both" like the actual Beatles and Stones would have said.
Anyway. These are called "alternative questions" and they are a specialty of 还是.
Now imagine rising intonation on both "Beatles" and "Stones." It's really a different question now (a friendlier one). There are no expectations. You can say "no" if you don't take an interest in 60s music at all; you can say "yes" (and then probably explain yourself).
To translate this, you would use 或者, which is "or" without the expectations. It does not form a question by itself; you have to tack on a 吗 to get a yes/no question ("polar question"), same as you do to turn any other statement into a question.
Just an answer with native instinct.
I would not use 或者 in this sentence. 还是 probably is about making a conscious, exhaustive choice. 或者 is just listing available options serially.
The main dish is pork or chicken. Would you choose pork or chicken?
In both of these sentences 或者 还是 are not interchangeable.