Atticus won't automatically add accents based on the language you're writing, but if you have imported the document, they will import. If you're writing within Atticus, you have a few options:
You can Google the keyboard shortcuts or Alt codes for the accent and Atticus should recognize them
You can open the Emoji Menu and check out the Latin Characters options in the General Punctuation section
Windows: Windows key and period dot
Mac: CTRL + CMD + Space
If the accent already appears in Atticus elsewhere, you can copy/paste it within the program