That can be done by adding the specific keyboard layout command into a
.desktop file saved in
~/.local/share/applications along the other desktop files that launchers like Synapse can therefore access.
The keyboard layout command to select a certain layout is like:
setxkbmap us intl
us with the desired language and
intl with variant if necessary.
For French it should be
setxkbmap fr. Etc. A list of all possible keyboard layouts and other parameters can be found in:
The desktop file should have a form similar to
Name=US - Keyboard US International dead Keys
Exec=setxkbmap us intl