It produces the full character as an independent letter. No modifier keys required. I press ‘2’ I get ‘é’. So yes, it could be utilized as it is not a dead key.
(PS- I see that yet again we had the same idea but I was late to the ball game. I reviewed your earlier post (with pictures, I’m an idiot). Sorry. 
)
Apology accepted, Romanos!
I do know that it’s possible to use whatever keyboard layout you like within macOS, and that Dorico just handles whatever character code it receives from the OS.
I know directly from Daniel that dead keys have been a nightmare for Dorico’s development team, and that Qt’s Multilingual keyboard support is buggy (and inconsistent).
I do know that at the point I was trying to make the Notation Express Stream Deck profile fully multilingual, dead keys were particularly problematic.
I don’t understand why dead keys on a German keyboard should cause problems when sending an undead (live?) character to Dorico. Logically it shouldn’t have anything to do with which language is set within Dorico’s Key commands dialog.
Just to be doubly sure; I did double check this, I was able to switch to the alternate layout, try and assign a key command and Dorico recognized the character perfectly. No modifier keys needed; it was interpreted correctly:
I’ve used Ukulele to remove dead keys from my norwegian keyboard (MacBook), and it works perfectly with Dorico. I don’t think the ‘Keyboard language’ menu in Dorico should make any difference, as long as your OS is set to use the correct layout. I think the items on this list are merely presets that the developers have tailored to those specific keyboards. It won’t “see” what keyboard you use, or what layout your OS is set to.
Romanos, try with alt-shift-1 on your azerty layout and you’ll see you cannot use it for shortcuts : that’s the diacritic acute accent 
Dear Romanos, as I said before, I use a custom modified keyboard:
When I type ⌥U in any other program on my Mac I get a character ū. To make sure - not just “-” or “u” but a full character ū. Exactly how I set it up.
When I type Lyrics in Dorico it produces a character ū as well.
When I am trying to set up a shortcut in Dorico, this key produces ⌥U
When I open my modified keyboard layout and press ⌥U, it doesn’t show that this key would be a dead key. Please see image IMG1413.jpg in my 4th post. But, I am still not able to set a shortcut to this combination.
A possible complication here, and a possible explanation of the conflicting results. There are basically two ways of encoding characters with diacritics in Unicode. In the Windows world it is usual to encode them as ‘precomposed’ characters: é = U+00E9, ü = U+00FC. In the Mac world, however, I understand that the other way is commonly used: é is encoded as a sequence of e (U+0065) plus a combining acute accent (U+0301), and ü as u (U+0075) folowed by a combining diaeresis (U+0308), so that the diacritic is a separate character and can actually be deleted separately from the base character. Could Dorico be having trouble attaching a keyboard shortcut to a keystroke in one case but not the other?
I just discovered another shortcut, which doesn’t work on my modified keyboard: ⌥S. My keyboard produces in this case a character š. It is not a dead key, anyway, it doesn’t work as well.
The reason Dorico produces the characters ⌥U is because you are pressing both keys to produce ū. The keys combine to give you the character that you want. The only way to use ū as a shortcut in itself is if that was the default character (on the base-layer of your keyboard) whenever you pressed the ‘u’ key (ie- you do not have to press a modifier).
What I was suggesting earlier was adding a different keyboard layout that had that character as the default base-layer. For instance, turning my keyboard to French azerty makes the 2 key produce é. In that case, I can assign é as a shortcut. But if I’m on my American layout, I have to press ⌥E+E (a second time) to produce the same character. If I were to do the same sequence in Dorico, Dorico would see ⌥E because that’s what I’m pressing. It appears that this is the situation you are in with ⌥U. So, it’s not that ū is a “dead key” it’s that you aren’t actually pressing ū, you’re really pressing ⌥U which just happens to produce that character.
Trying to follow your thoughts. Any way I am not sure I understand…
I do not have a task to assign some shortcut to this particular letter ū. My task is to set in Dorico a shortcut Alt+U no matter what an output it will produce. As my custom LT-layout is based on a German default, I guess Dorico still interprets a combination Alt+U as a dead key. In a small gif you can see, that in a custom LT-layout it wont be showed as a dead key. Any way if it set in Dorico, it doesn’t produce any output…
