I thought the premise, with Harry's almost total aphasia, was fascinating, and you did a good job presenting the frustration and despair Harry felt, the sense of isolation and hopelessness. The idea of being almost completely unable to communicate is horrifying, even more so when the mind inside is as active as ever, and you convey that sensation of trapped fear and anger very well.
I also found your Snape's reaction to Harry's predicament quite in character; he's just the kind to berate Harry for 'hiding out', and to basically bully him into working on getting better. I especially liked the fact that while Snape was trying to help Harry, Harry was also trying to help Snape; they're both so damaged, in so many ways, that it's good to see them *both* getting some care and nurturing (though Snape's version is rather 'tough love' most of the time.)
I did sometimes find the word choice or phrasing awkward or confusing, and I though the ending was a little rushed. I would have liked more development of the relationship rather than the abrupt leap into intimacy at the end. In particular, I think it would be fascinating to see what tricks and techniques the two of them come up with to communicate with each other. Legilimency, maybe?
I do appreciate the fact that there is no sudden, miraculous cure, and overall this was an intriguing, original postwar romance.