As one fellow TV reporter asked the stars of “The Americans” earlier this year, “Remember when Russian infiltration was a cute little thing we were able to contain to the ’80s?” Yes, the fifth season of “The Americans” arrives with a weird sense of timeliness. But the Cold War spy thriller, however, will continue to focus inward, on Paige Jennings , who recently learned that her parents are deep-cover Russian spies and who, though still very troubled by the news, is starting to take some interest in the family biz.