An old-fashioned solution?
st2[l_] :=
l[[1, 1]] <> " is " <> ToString[l[[1, 2]]] <>
Table[" and " <> l[[n, 1]] <> " is " <> ToString[l[[n, 2]]], {n, 2, Length[l]}]
st2[{{"a", 1}}]
"a is 1"
st2[{{"a", 1}, {"b", 2}}]
"a is 1 and b is 2"
st2[{{"a", 1}, {"b", 2}, {"w", 5}, {"x", 10}}]
"a is 1 and b is 2 and w is 5 and x is 10"