I'd like to point out a difference between American English and British English here: When a woman from a French-speaking country continues to be be referred to by the French title rather than Mrs., that title is generally spelled with a period (full stop). You can see this in the online Encarta, American Heritage, and Random House dictionaries--Merriam-Webster's dictionary gives Mme without the period. The title Mlle, also occasionally used instead of Miss for a girl or woman from a French-speaking country, is also shown with a period in the first three dictionaries and without a period in the M.-W. dictionary, except that the Random House adds Mlle (without a period) as a variant spelling.M. Mme. & Mlle
Also, I think the word madame is abbreviated without the period because the abbreviation ends with the same letter as the word. Earlier today, I was trying to remember the abbreviation for the plural form of monsieur which is messieurs. Can someone please tell me? Thanks! (...)
As the Wikipedia article "International English" states, it is a concept, not an actual set of standards. As the article says,It's Mr and Dr without the period in International English, because it's a contraction abbreviation. The Bristish still use period to abbreviations that are truncated. I guess americans just don't care about the rules.
One can hardly blame Americans for failing to follow a standard which does not actually exist. As previously noted, we have our own standard--and, as such standards go, a quite strong one--for the punctuation of such abbreviations as Mr. and Dr.Sometimes "international English" and the related terms above refer to a desired standardisation, i.e. Standard English; however, there is no consensus on the path to this goal.
I have always seen it as "Messrs":Maître, I imagine, as that is the title for a lawyer.
AS an interesting side point; the English have invented their own abbreviation for Messieurs - Mssrs. It is (or used to be) used in company names.