Browsers are configured with a "Locale" this can be configured in your browser. The language can be set such as fr (French), fr-be (Belgian French), fr-ca (Canadian French), etc. This information is sent in the header information of the HTTP request. Delta's web site reads the header value and then re-directs your browser to a URL that contains a language parameter. The server-side applications produce output in the specified language (if the language is supported).

I can't help you with IE but with Firefox
Tools > Options > Advanced > General > Languages

If you log in using your SM number the prices will be displayed in your home currency but the language set in the browser is honored. This accomdates non-English speaking users who reside in the U.S; or an other example would be an U.S. ex-pat living in France but browsing in English.

Try setting the language to "fr". The majority of the page contents will be in French but the prices will be in US $ if your home address is the US.

Try shopping without logging in. The language will remain French (using my example) but the prices will be in Euros. If you choose fr-ca the prices will be in Canadian dollars.

You can book using your CC without entering your SM number. When finished, you can call DL and add your SM number to the itinerary. To view the itinerary you will need the conf#. Or, you can add your SM# when you check in. You might be able to log in and pull up the conf# and add your SM # on line but I can not confirm this.

You might have a problem booking a ticket in Euros using a CC that has an "anchor" address in the U.S. Please let us know.