In your localization file make the string something like this:
StringKey = {0} attacks for {1} damage!
Then when you use that string use something like the following:
LabelText.text = string.format(Localization.Localize("StringKey"), Attacker.Name, amtDamage);
This should produce something like "Ranger attacks for 3 damage!" if the name was Ranger and the amtDamage variable was 3.