I’m rereading Jane Eyre , wherein there is a character whose surname is St. John. I recall some years ago in a British film or two it being pronounced something like “sin’ shan.”
Is that the proper pronunciation of this name? If so, why?
Is this just in England?
Is it the current pronunciation, or one used only in earlier times?
Is anybody today actually given that as a first name?
Why? 
I’d always heard it pronounced like "singein’ ". and I don’t have any idea why or where it comes from , but I always thought it would be a pretty cool name. Years later I heard about an althlete (volley ball player, surfer?)who spells his name(I think) Syngin or Cingyn. Hell, I don’t know. I still think It counds cool, if a little stage namey.
That would be Sinjin Smith, beach volleyball player, and former partner of Karch Kiraly.
I gather it was pronounced that way because the English like to do that. It’s like Worcestershire and Marylebone. I don’t know if anyone is named that now, but there were a couple of other St. names. In Five children and It, the baby’s real name is St. Maur, though how that is pronounced I haven’t a clue.
1/ It is the ‘proper’ pronunciation if a given name, otherwise as in the ordinary saints name as a surname.
2/ In the whole of the Uk and even now (according to Google) as an increasingly popular given name, respelt as sinjun or sinjon etc…
3/ Current and historic. If I saw it as a given name I would assume Sinjun as the pronunciation.
4/ It is usually given as an historic family surname as a second or third given name.
Google suggests that the athlete mentioned above is actually called St John as asecond given name but has adopted it as his main given name and respelled it.
The pronunciation is not that odd, given the English tendency to swallow 't’s and to make all vowels sound like uh. That gives Sainjun as a fairly obvious slurred pronunciation. It is thought that the Scottish surname Sinclair comes from a similar elision of St Clair.
Now take the surname Menzies that is often prnounced mingis and work with that for a bit!
NB. I have omitted all reference to Monty Python Luxury Yachts and Mangrove Throat Warblers, leaving this to someone sadder than I.
I’ve heard it pronounced *see-more * (like Seymour).
Knowing the British, probably “SinWorcestershire.” 
A local told me that Sault Ste. Marie is pronounced “Soo Set Marie.” I’m still shaking my head over that one.
For the sake of familiar occurences, there’s the character of Jerry St Clair in Phoenix Nights - which seems to be there solely to give him the nickname ‘the Saint’. (Acutally, now I think about it, I’m not sure how his surname was spelt when he got his name above the door…anyone got a DVD?)
I seem to remember reading that a character on Airwolf was named “St. John” (his first name, no less), and it was pronounced something like “sin jin.”
In the Roger Moore 007 flick “A View to a Kill” Bond goes by the pseudonym James St. John-Smith, which he pronounced “Sinjin Smythe”.
The example that comes to my musical mind is Brian Peter George St. John de la Salle Eno. (Can you believe I typed all that from memory? Was it accurate?) The “de la Salle” part sounds so French, maybe the St. John part next to it gets a French pronunciation, se~ zha~, nasalizations and all.
One more vote for the “sinjin” pronunciation. I first heard it from a high school English teacher when my class read Jane Eyre, and it caused a fair amount of confusion.
What about
Featherstonehaugh = Fanshaw
It’s not a French or pseudo-French pronunciation. It’s quite different from that, with a hard J sound. (See Four Weddings and a Funeral for Rowan Atkinson’s hapless vicar struggling with the name)
In the film ‘Maurice’ this name was pronounced ‘Feestinhay’ (by an Oxford dean).
I assume the pronunciation is Anglicised from the French, which would be something like “Sew San Marie.”
But I think it’s at least influenced by French pronounciations, as **Johanna **implies. The French “saint” is pronounced a little like “san,” with a short, nasal “n,” and is reminiscent of the “sin” part. And IMO, “jin” more closely matches the French “Jean” than the English/American “John.” Given England’s history and its roots of Norman, French-speaking rule, it’s at least likely to me that there’s a French influence in this pronounciation.
It’s an anecdote, but I’ll the Brits I’ve heard that have spoken any French at all tend to have an excellent grasp of the French accent (probably due to proximity), far better than the Americans I’ve attended classes with. Take that for what it’s worth.
When I visited Alnwich Castle I was surprised to find out that it is “Anock” Castle not my tongue-twister pronunciation.