Edit /etc/default/keyboard as shown below.

coolermaster.com Quick Fire Stealth

newegg.com CM Storm QuickFire Stealth

Compact “tenkeyless” (aka TKL or 80%, no numeric pad) 87-key layout. Features a frameless design with a minimal desktop footprint

        Brand Cooler Master
        Name CM Storm QuickFire Stealth
        Model SGK-4000-GKCM2-US
        
        87 Keys (no 10-key pad)
        Keyboard Interface USB or PS/2
        Design Style Mini
        Key Switch Type Brown Cherry MX
        Keyboard Color Black
        Type Wired
        
        Mechanical CHERRY MX switches
        Extremely compact size
        Covert keycaps
        Removable braided USB cable
        

wikipedia.org AltGr key

lists.x.org/archives International US keyboard - AltGr deadkeys

tylercipriani.com Toward a More Useful X Keyboard

viliampucik.blogspot.com US International Keyboard

To enable typing of international characters with AltGr key while using US layout:

        Some useful key combinations:
        
        á ← AltGr+a
        ä ← AltGr+q
        č ← Shift+AltGr+.+c
        ď ← Shift+AltGr+.+d
        é ← AltGr+e
        í ← AltGr+i
        ĺ ← AltGr+'+l
        ľ ← Shift+AltGr+.+l
        ň ← Shift+AltGr+.+n
        ó ← AltGr+o
        ô ← AltGr+6+o
        ŕ ← AltGr+'+r
        š ← Shift+AltGr+.+s
        ť ← Shift+AltGr+.+t
        ú ← AltGr+u
        ý ← AltGr+'+y
        ž ← Shift+AltGr+.+z
        £ ← Shift+AltGr+4
        € ← AltGr+5
        ¥ ← AltGr+-
        © ← AltGr+c
        ° ← Shift+AltGr+;
        ¶ ← AltGr+;
        

scottseverance.us “English (intl., with AltGr dead keys)” keyboard layout

linoxide.com/ How to Configure Keyboard on Ubuntu 18.04

wiki.archlinux.org Xorg/Keyboard configuration

wiki.archlinux.org Linux console/Keyboard configuration

/etc/default/keyboard - this works

XKBVARIANT=”intl” or “altgr-intl”

        XKBMODEL="pc105"
        XKBLAYOUT="us"
        XKBVARIANT="altgr-intl"
        XKBOPTIONS=""
        
        BACKSPACE="guess"
        

/usr/share/X11/xkb/rules/base.lst

        ! model
        
        ! layout
        
        ! variant
        
        ! option
        

thoughtco.com/ How To Make Spanish Accents and Symbols in Ubuntu Linux

The USA International (with dead keys) layout gives you a second method of typing the accented letters, as well as the only method for Spanish punctuation. This method uses the RightAlt key (usually to the right of the space bar) pressed at the same time as another key.

The following match AltGr-intl

        RightAlt-
        RightAlt-shift-
        
        RightAlt-a á
        RightAlt-shift-A Á
        RightAlt-e é
        RightAlt-shift-E É
        RightAlt-i í
        RightAlt-shift-I Í
        RightAlt-n ñ
        RightAlt-shift-N Ñ
        RightAlt-o ó
        RightAlt-shift-O Ó
        RightAlt-u ú
        RightAlt-shift-U Ú
        RightAlt-y ü
        RightAlt-shift-Y Ü
        RightAlt-/ ¿
        RightAlt-shift-! ¡
        RightAlt-[ «
        RightAlt-] »
        

Log altgr-intl keys on ivie Debian 9.9 stretch

        Tue Jul  2 14:27:26 MDT 2019
        Release:	9.9
        Codename:	stretch
        
        rightalt-
        RightAlt-shift-
        
        RightAlt-1 ¹
        RightAlt-2 ²
        RightAlt-3 ³
        RightAlt-4 ¤
        RightAlt-5 €
        RightAlt-6 dead
        RightAlt-7 dead
        RightAlt-8 dead
        RightAlt-9 ‘
        RightAlt-0 ’
        RightAlt-- ¥
        RightAlt-= ×
        
        RightAlt-shift-1-!  ¡
        RightAlt-shift-2-@ dead
        RightAlt-shift-3-# dead
        RightAlt-shift-4-$ £
        RightAlt-shift-5-% dead
        RightAlt-shift-6-^ ¼
        RightAlt-shift-7-& ½
        RightAlt-shift-8-* ¾
        RightAlt-shift-9 dead
        RightAlt-shift-_ dead
        RightAlt-shift-+ ÷
        
        RightAlt-q ä
        rightalt-w å
        rightalt-e é
        rightalt-r ë
        rightalt-t þ
        rightalt-y ü
        rightalt-u ú
        rightalt-i í
        rightalt-o ó
        rightalt-p ö
        rightalt-[ «
        rightalt-] »
        rightalt-\ ¬
        
        RightAlt-shift-Q Ä
        RightAlt-shift-W Å
        RightAlt-shift-E É
        RightAlt-shift-R Ë
        RightAlt-shift-T Þ
        RightAlt-shift-Y Ü
        RightAlt-shift-U Ú
        RightAlt-shift-I Í
        RightAlt-shift-O Í
        RightAlt-shift-P Ö
        RightAlt-shift-{ “
        RightAlt-shift-} ”
        RightAlt-shift-| ¦
        
        RightAlt-a á
        RightAlt-s ß
        RightAlt-d ð
        RightAlt-f f
        RightAlt-g g
        RightAlt-h h
        RightAlt-j ï
        RightAlt-k œ
        RightAlt-l ø
        RightAlt-; ¶
        RightAlt-' dead
        
        RightAlt-shift-A Á
        RightAlt-shift-S §
        RightAlt-shift-D Ð
        RightAlt-shift-F F
        RightAlt-shift-G G
        RightAlt-shift-H H
        RightAlt-shift-J Ï
        RightAlt-shift-K Œ
        RightAlt-shift-L Ø
        RightAlt-shift-: °
        RightAlt-shift-" dead
        
        RightAlt-z æ
        RightAlt-x œ
        RightAlt-c ©
        RightAlt-v ®
        RightAlt-b b
        RightAlt-n ñ
        RightAlt-m µ
        RightAlt-, ç
        RightAlt-. dead
        RightAlt-/ ¿
        
        RightAlt-shift-Z Æ
        RightAlt-shift-X Œ
        RightAlt-shift-C ¢
        RightAlt-shift-V ®
        RightAlt-shift-B B
        RightAlt-shift-N Ñ
        RightAlt-shift-M µ
        RightAlt-shift-< ç
        RightAlt-shift-> dead
        RightAlt-shift-? dead