gamekit exchanges and localization across iOS/macOS platforms

i'm trying to use exchanges and localization. i'm getting different results on iOS versus on macOS.

i have the following line in my Localizable.strings (English) file

"emote_message_hello" = "hello";

here's my sendExchange function:

gkTurnBasedMatch.sendExchange(to:[opponent],
                   data:Data(),
                   localizableMessageKey:"emote_message_hello",
                   arguments:[],
                   timeout:TimeInterval(1))

and here is my receivedExchangeRequest function

  func player(_ player:GKPlayer, receivedExchangeRequest exchange:GKTurnBasedExchange, for gkTurnBasedMatch: GKTurnBasedMatch) {
    print("\(exchange.message)")
  }

on macOS this outputs "hello". yet the same code on iOS outputs "emote_message_hello". in other words it appears that macOS is automatically localizing the string, while iOS is not.

am i doing something wrong or is this a bug?