Help for this page
perl -pe 's/^([^"]+)"(.+)"/($x = $2) =~ y{\t}{,}s;"$1\"$x\""/e'
a b c d "x1 x2" c d e "x2" e f h "x3 x4 x5 x6"
a b c d "x1,x2" c d e "x2" e f h "x3,x4 x5,x6"