"The animal is weak because it has not been eating."
Translation:To zvíře je slabé, protože nejí.
"To zvíře je slabé, protože ono nejdelo" is very strange, there shouldn't be the world "ono" because we've already pointed out what is the subject of this sentence in the first two words.
It is not the preferred translation. You can see the oficial preferred translation above. It is just one of the accepted translations because it is not impossible.
nejí seems like a poor translation to me...it doesn't give any sense that the lack of eating is in the past. Can someone explain why present is preferred to say, nejedl or nesnědl? We've also been taught that žrát is the verb to use for animals eating...
That is how Czech works. "nejí" can mean all of "is not eating right now", "does not eat (ever)", "has not been eating".
A Czech speaker had no problem saying "Nejí už týden." "He hasn't been eating for a week (already)."
Nesnědl is impossible here, it is perfective and is used to rall you ate something (and not just a part of it, the food is now eaten and not available any more).
Nejedl is also possible here, there is no 1:1 mapping of Czech and English tenses.
Often you would distinguish: "Nejí už týden." The person has been ill and has not been able to eat or intentionally has been rejecting food.
"Už týden nejedl." The person didn't have any food to eat, but also it can be the illlness so he has not been able to eat.
You can use both jíst and žrát here.
I've already gathered that Czech can often use the present if there is some other word that indicates the action was past (i.e., už), but it makes sense that if the present is that flexible already it might be more flexible.
Thanks for the tip on the perfective.