I would think that as he spent a lot of his earlier life in such places, the word 'institution' would be one that JH would have known only too well.
Woffinden (P 91) illustrates what he describes as JH's basic inarticulacy when he describes France as 'someone who learned me previous occasions when I was younger'. I don't think this brief passage is all that inarticulate, to be honest, certainly no worse that what I hear kids shouting at each other these days. I don't recall anyone in any of the books being referenced as saying that they couldn't understand him or what he was talking about. He may well have stumbled over his words when under the severe and unimaginable pressure of the court-room, but I don't get the basic impression that in everyday life his diction and use of English was anything out of the ordinary. I may be wrong, of course.....as a Midlander I have always had trouble in fully understanding the modern-day London accent, something which the BBC and southern English people in general may well find difficult to understand in turn.
We are suffering from a plethora of surmise, conjecture and hypothesis. - Sherlock Holmes, The Adventure Of Silver Blaze