If you use HTML, it’s easy!

Use the HTML character codes instead of direct letters. For a reference, please refer to e.g. http://www.il-st-acad-sci.org/codes.html

For example, instead of
INFECTÉ:
xxx: À été effacé du message.

you would have
INFECTÉ:
xxx: À ét&eacute effac&eacute du message.

Hope this helps,
Vlk