Allow only one . (dot) to Regex

I am using below regex for my project to validate customer name.

ALPHA_SPECIAL_CHAR = /^[a-zA-Z'"-sçéâêîôûàèìòùëïüÇÉÂÊÎÔÛÀÈÌÒÙËÏÜ]+$/

Now I want to add new requirement which will allow only one dot (.) to this regex. How to modify this existing regex.

E.g

name = JOHN. // this should be valid
name = JOHN.. // this should be invalid