A most unsociable dog he proved to be (он оказался очень необщительным псом; to prove — доказывать; оказываться
), resenting all their advances (отвергающим все их попытки завязать более тесные отношения; to resent — негодовать, возмущаться; обижаться; advance — сближение /с кем-либо; попытка завязать более тесные отношения/), refusing to let them lay hands on him (отказывающимся позволять им касаться его), menacing them with bared fangs and bristling hair (угрожая им обнаженными клыками и вздыбленной шерстью). Nevertheless he remained (тем не менее он остался), sleeping and resting by the spring (спал и отдыхал у родника), and eating the food they gave him (и ел еду, которую они давали ему) after they set it down at a safe distance and retreated (после того как они ставили ее на безопасном расстоянии и уходили). His wretched physical condition explained why he lingered (его плачевное физическое состояние объясняло, почему он медлил = причину его промедления); and when he had recuperated (а когда он поправился), after several days' sojourn (после нескольких дней пребывания), he disappeared (он исчез).
A most unsociable dog he proved to be, resenting all their advances, refusing to let them lay hands on him, menacing them with bared fangs and bristling hair. Nevertheless he remained, sleeping and resting by the spring, and eating the food they gave him after they set it down at a safe distance and retreated. His wretched physical condition explained why he lingered; and when he had recuperated, after several days' sojourn, he disappeared.
And this would have been the end of him (и это было бы развязкой /истории/ о нем; end — конец; развязка
), so far as Irvine and his wife were concerned (насколько это касалось Ирвина и его жены), had not Irvine at that particular time been called away into the northern part of the state (если бы Ирвина в это конкретное время = как раз в это время не отозвали в северную часть штата). Riding along on the train (когда он ехал в поезде), near to the line between California and Oregon (возле границы между Калифорнией и Орегоном), he chanced to look out of the window (он случайно выглянул в окошко; to chance — происходить, случаться) and saw his unsociable guest sliding along the wagon road (и увидел своего нелюдимого гостя, плавно скользящего вдоль железнодорожных путей), brown and wolfish (бурого и похожего на волка), tired yet tireless (усталого и все же неутомимого), dust-covered and soiled with two hundred miles of travel (покрытого пылью и грязного от двухсот миль пути).
And this would have been the end of him, so far as Irvine and his wife were concerned, had not Irvine at that particular time been called away into the northern part of the state. Riding along on the train, near to the line between California and Oregon, he chanced to look out of the window and saw his unsociable guest sliding along the wagon road, brown and wolfish, tired yet tireless, dust-covered and soiled with two hundred miles of travel.