If its just a few invocations then just chain them. Otherwise I guess I'd try this:
Seq("a" -> "b", "b" -> "a").foldLeft("abab"){case (z, (s,r)) => z.replaceAll(s, r)}
Or if you like shorter code with confusing wildcards and extra closures:
Seq("a" -> "b", "b" -> "a").foldLeft("abab"){_.replaceAll _ tupled(_)}
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…