Problem with mapping a key to multiple characters (Unicode + diacritic symbol)

[Pierre-Luc Angles]

Dear list-members,

I allow me to write to you because I am now creating / mapping two 
different keyboard layouts, one for the transliteration of Ancient 
Egyptian and the other for a special Greek polytonic keyboard used by 
people reading ancient Greek documents. I have problems with these two 
new keyboards.

First, I would like to solve my problem with the transliteration of 
Ancient Egyptian.

I read in the archive of this list this thread (cf. 
https://lists.freedesktop.org/archives/xorg/2009-January/042282.html) 
and that is why I have created a file ~/.XCompose, with contents

<i_breve_below> : "i̯"
<u_breve_below> : "u̯"
<ı_ring_above> : "ı͗"
<I_ring_above> : "I͗"
<č_dot_below> : "č̣"
<Č_dot_below> : "Č̣"
<s_macron_below> : "s̱"
<S_macron_below> : "S̱"
<H_macron_below> : "H̱"
<h_circumflex_below> : "h̭"
<H_circumflex_below> : "H̭"

When I modify for example my keyboard layout like this
:

key <AE01>	{ [        ampersand,                1,        i_breve_below, 
			      U032F ] };

the i_breve_below does not work and function, I think, as if it would be 
“NoSymbol” instead of this.

For information, I am using Linux Manjaro 4.19 XFCE and scim is not 
enabled and not downloaded on my laptop.

I would be very nice if you could me help somehow to solve this problem.

I thank you in advance a lot.

Best regards,

Pierre-Luc