I think the more common English translation would be "I am going to look good ON vacation." The preposition choice in American English would use "on" rather than "in" unless I misunderstood the sentence.
It should be ."...look well" since after a verb you need an adverb (well) and not an adjective (good). Am I pedantic? Or wrong?
This sentence illustrates again the importance of choosing vocabulary which allows for a straight word for word translation if the course designed is based on the translation method. I am very grateful to Duolingo for providing so many language courses, but the methodology is many years out of date (though probably the easiest for the on-line medium). That said, a little more care in selecting the sample sentences would not be a bad idea.
Such a choice would limit the sentences taught to only a terribly limited set of structures, wouldn't it? Just as an example, Catalan constructs the present perfect with the verb to go (as most of the other Romance languages, along with English and other Germanic languages, construct a future tense). Would that mean that you would have to leave the present perfect entirely out of the Catalan program? Would it mean that the English from Russian program would have to use only sentences that did not use any determiners? How could one have a Japanese program for anything but Korean speakers?