The Basel Committee on Banking Supervision describes itself as the primary global standard setter for bank regulation. It is based in Basel, Switzerland. When I first started work, the usual English name for the Committee contained the spelling Basle, rather than the German spelling Basel.
Oddly, though, although the English spelling contains an <s>, the normal English pronunciation is similar to the French Bâle, with a long [a]. The circumflex in French often indicates that an [s] was present in the past, so no doubt the English spelling was adopted when French still retained the [s], in either pronunciation or spelling. Presumably, the English pronunciation reflects the diplomatic prestige of French.
When I started writing this post, I did remember that in the 1970s and early 1980s I had generally heard the French pronunciation [Bâle] in English, for both the town and the committee. So until I checked, I didn’t remember that the traditional English spelling includes an [s]. The BBC Pronunciation Unit confirms the standard English spelling (with an [s]) and pronunciation (with no [s]). BBC – Magazine Monitor: How to say: Basel/Bâle/Basle/Basilea
By the way, the Italian name is Basilea.
Change of name
In the late 1990s, one member of a consultative group I worked with was from the Bank of England and representing the Committee. At that time, we were still calling it the Basle Committee. He told us at one meeting that the Committee was now describing itself in English as the Basel Committee, no longer as the Basle Committee.
In The Basel Committee on Banking Supervision: A History of the Early Years, 1974–1997, Charles Goodhart (2011) says that this change was made in 1998 during negotiations with the local government.
The change didn’t surprise me. Although Basel is near the French speaking part of Switzerland, both the canton and town of Basel are firmly German speaking.