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

[Pierre-Luc Angles]

Dear Ilya, dear Walter, dear all,

thanks for your precisions!

Since it can cause problems with updates, I will try with the first 
possibilities that Ilya kindly mentioned and let modifications in 
/etc/profile aside.

I would like also to know if there are possibilities for using directly 
these composed keys not just only in LibreOffice but for example in Firefox.

I would like also to mention that launching env XMODIFIERS='' 
GTK_IM_MODULE=xim libreoffice in my terminal results in the following 
messages as soon as I open LibreOffice Writer:

~/.config/libreoffice/4/user/uno_packages/cache/uno_packages/lu28588zw1mep.tmp_/Grammalecte-fr-v0.6.5.oxt/pythonpath/grammalecte/fr/gc_engine.py:360: 
FutureWarning: Possible nested set at position 2
   rule[0] = re.compile(rule[0])
~/.config/libreoffice/4/user/uno_packages/cache/uno_packages/lu28588zw1mep.tmp_/Grammalecte-fr-v0.6.5.oxt/pythonpath/grammalecte/fr/gc_engine.py:360: 
FutureWarning: Possible nested set at position 1
   rule[0] = re.compile(rule[0])

Grammalecte is an correcter addon/plugin that I have installed in 
LibreOffice.
It seems to cause no problem but I do not understand these messages... I 
hope that I do not exaggerate with your patience.

Best,

Pierre-Luc