Replacement by dictionary possible with AWK or Sed? [closed]

Answer 1

$ awk 'NR==FNR{map[$1]=$2;next} { for (i=1;i<=NF;i++) $i=($i in map ? map[$i] : $i) } 1' fileA fileB
one one hello hallo two three hallo fem fem

Note that it will compress any chains of contiguous white space to a single blank char. Tell us if that is an issue.