Comment 95 for bug 1045914

Just set org.gnome.desktop.input-soures.sources to [('xkb','us'),('xkb','<lng1>'),('xkb','<lng...'>)]

Reason: open up /usr/share/gnome-shell/ui/panel.js, realize that

const PANEL_ITEM_IMPLEMENTATIONS['keyboard'] = imports.ui.status.keyboard.InputSourceIndicator;

Check /usr/share/gnome-shell/ui/status/keyboard.js and find

const DESKTOP_INPUT_SOURCES_SCHEMA = 'org.gnome.desktop.input-sources';

const InputSourceIndicator = new Lang.Class({
//...
// see where and how DESKTOP_INPUT_SOURCES_SCHEMA is used
//...
)};