Hi, so after a while I figured out.
Go to Add a Language and select interlingue.
Then click it, go to Options
You get one default layotu like QWERTY - something.
Remove the default one (click it, then press remove)
And then "Add a keyboard"
Unitet States-International should appear on that list.
Then of course, select the layour interlingue as you keyboard layout on the previous screen