Removing multiple character types from a string

There would be no significant difference, since there is only 3 characters to remove and no so big string to filter, but you may consider to use Set for this purpose. E.g.

val toRemove = "ilr".toSet
val words = sentence.filterNot(toRemove)

I'd just use Java's good old replaceAll (it takes a regexp):

"Twinkle twinkle little star, oh I wander what you are" replaceAll ("[ilr]", "")
// res0: String = Twnke twnke tte sta, oh I wande what you ae

In contrast to working with chars (as in filtering a Seq[Char]), using regular expressions should be Unicode-safe even if you're working with code points outside the basic multilingual plane. "There Ain't No Such Thing As Plain Text."