Not an answer, rather a comment. The 'sal-le' example, quite known, does not seem very impressive to me. Not only because it's rather a rare-artificial word, but also because "can't be written" is a too strong expression: it's just that the normal rules for spanish phonetic rules (which are almost totally rigid) would have an exception. But the context could enough hints to this.
This is not exactly another example, but a related case: the 'sh' sound. In Spanish, we don't have that sound at the end of words (as in 'spanish') and so we can't write that (the 'y' at the end of the word is pronounced as 'i'). However, by the influence of english and also by the need of write the interjection 'sh' (the sound we make to ask for silence), we are quite used to read/write the digraph 'sh' to mean that sound. You could say that this pronunciation is an 'extended rule' to the standard Spanish rules.
In spite of this, we don't have any problem when the 'sh' group appears 'accidently' in normal Spanish, as in 'deshonesto' 'deshabilitado'.