> Once they've learnt the letters predicted by each token, they'll be able to do this for any word (i.e. token sequence).

They often fail at things like this, hence the strawberry example. Because they can't break down a token or have any concept of it. There is a sort of sweat spot where it's really hard (like strawberry). The example you give above is so far from a real word that it gets tokenized into lots of tokens, ie it's almost character level tokenization. You also have the fact that none of the mainstream chat apps are blindly shoving things into a model. They are almost certainly routing that to a split function.