> perl -de0
...
  DB<1> @a = qw(Russia Russia's Russias Russian)

  DB<2> $wordstem = "Russia"

  DB<3> x grep { /\bwordstem(s|\'s|n)?\b/i } @a
  empty array

  DB<4> x grep { /\b$wordstem(s|\'s|n)?\b/i } @a
0  'Russia'
1  'Russia\'s'
2  'Russias'
3  'Russian'