The translation I see is a perfectly valid English translation. If I say "you either stay or you go" to someone, I'm not exactly describing what's happening now, but talking about their potential future actions. It's one of those phrases where, although correct, the future tense part of the sentence is superfluous and often omitted.
The trick here is getting the balance right between literal translation and the natural English equivalent. Pretty sure if I was blitzing through a skill strengthening session and I came across this sentence, I would type "you either stay or you go" or "you will either stay or go". The latter is even less literal, but still holds the same meaning. At speed I doubt I'd even think about your suggestion because it is less natural, even though it is technically correct.
At a beginner or intermediate stage, this sounds more like rationalized sloppiness. Learn and actually follow the rules first and then let the context of interacting with native or highly fluent speakers, such as Kenyans and Tanzanians, show you what can slide and have equal meaning in real social context. The context of exercises, fast or slow, has very limited usefulness and runs a real risk of developing bad habits in learners that will have to be overcome with difficulty later.
From my experience as a teacher I'd rather say it is more useful to memorise expressions according to how they would be naturally used by native speakers in certain contexts, rather than sticking to the grammatical rules and translating everything word by word and tense by tense. ( although I also find it very annoying when I am very proud that I know every single word and understand every single structure, and then the actual translation is something completely different from what I was expecting) Following the rules during the course, and then having to break your rules and adapting to how native speakers actually speak is contra-productive. Duolingo is a very good app for this reason, i.e. it encourages you to memorise useful phrases ; the only problem is that the English translations are written by native speakers of the target language, and not native speakers of English. and considering that Kenya and Tanzania were British colonies and most people there speak relatively good English, they probably still have among the best English translations on duolingo.. I wonder how the translations look like when you learn Japanese or Turkish...
I agree. I like the balance of being given enough information to know the correct forms but also the opportunity to hear what is (hopefully) normal talk. I can look at the rules and do verb conjugations or memorize lists on my own but I can't know what the typical shortcuts are that could help me sound less "tourist-y."
Personally, I would go for the most natural English translation, "You either stay or you go". For this question it is listed above as the correct answer, and maybe they also accept the future tense. (No one here said the future tense "you will either stay or you will go" is marked as incorrect.)
However, there are plenty of questions in this course where only the literal translation is marked as correct. If you write a natural English translation and it is rejected, I suggest reporting "My answer should have been accepted" and eventually, they will add it.