“a hundred days of sermonizing, one fart” → a metaphor for how something that one has put great effort into can come to nothing after even a slight mistake, much as a hundred days of serious spiritual study can be lost to the winds

a foreigner, a person from a foreign country; an alien, a foreign national / a person who is not Japanese

the Grand Duchy of Luxembourg

deceptive advertising; misleading advertising that exaggerates a product's merits

the United Arab Emirates

(literally) know the other side and yourself, a hundred battles will not be perilous

万国の労働者よ、団結せよ: workers of the world, unite!