I bit the bullet and have actually purchased a copy of the standard. (DIN 2137-1:2020-11)
Frustratingly, the legal agreements around buying DIN standards don’t let me reproduce the whole thing, but the keyboard images themselves aren’t considered normative.
The specific text about what’s allowed under the standard is:
Alternatively to the graphic symbols specified in ISO/IEC 9995 or described in Annex B, the appelations or abbreviations given in Table A.1, in Annex A can be used.
Sadly, they don’t actually define abbreviations for most keys.
Alt, Num. and Esc are all “standard”.
“Alt Gr” is acceptable, but is no longer preferred - The standard recommends use of Grᵃ instead.
“Strg” of course for Control.
The following full names can be used, but obviously do not work for us:
- Alternativ-Funktion wählen
- Ebene 2 wählen; Umschalttaste
- Ebene 3 wählen; Grafikzeichentaste
- Gruppenumschaltung; Extra-Wahltaste
- Eingabe
- Feststellen
- Großschreibung feststellen
- Rückführen/Neue Zeile
- Rückwärtsschritt
- Rückwärtsschritt mit Tilgen/Entfernen
- Steuerungsumschaltung wählen
- Tabulation links
- Tabulation rechts
- Superselekt
- Sekundär-Superselekt
- Numerische Eingabe feststellen
- Abbrechen
- Bildschirmanzeige drucken
- Escape
- F1 bis F12
- Pause
- Rollen
The symbols in Annex B are:
The best free resource I can find for ISO 9995-7 is: Category:ISO 9995-7 symbols - Wikimedia Commons
As far as I can tell, these do match what’s in the standard.