So, Wilbur can't talk when in shipwrecked. However, using the seaworthy (whatever its called) you can play as him in RoG. When examining the gravestones, he will talk normally like other characters. There are also many other weird things that happen when playing as SW characters in normal don't starve. It's a blast 
Steps to Reproduce
Play as Wilbur the monkey in SW. Find or spawn in the seaworthy structure and teleport to a RoG world. Then, simply examine a gravestone to make him talk.
Play as Wilbur the monkey in SW. Find or spawn in the seaworthy structure and teleport to a RoG world. Then, simply examine a gravestone to make him talk.
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A developer has marked this issue as fixed. This means that the issue has been addressed in the current development build and will likely be in the next update.