This is an adaptation of the Xorg US keymap "altgr-intl" variant for OSX. More information can be found here and here.
sudo cp us-altgr-intl.keylayout /Library/Keyboard\ Layouts
A reboot is probably necessary for the new keymap to appear in Preferences/Keyboard.
This has been tested with OSX Mojave 10.14.6.
Basics are here for my own usage but diacritics combinations (dead-keys mode overlappings) are probably missing. Any improvement is welcome. This file has been developped with Ukulele for a US ANSI keyboard.