From the Compose key Wikipedia page: A compose key (sometimes called multi key) is a key on a computer keyboard that indicates that the following (usually 2 or more) keystrokes trigger the insertion of an alternate character, typically a precomposed character or a symbol. In Linux, the default compose key combinations are in /usr/share/X11/locale/en_US.UTF-8/Compose. In order to add custom compose key combination, create ~/.XCompose, where the first line is include "%L" in order to include the default combinations. Here is the content of my ~/.XCompose: include "%L" # from /usr/share/X11/locale/en_US.UTF-8/Compose <Multi_key> <asterisk> <asterisk> : "⁂" U2042 # ASTERISM <Multi_key> <3> <e> : "з" U0437 # CYRILLIC SMALL LETTER ZE <Multi_key> <3> <E> : "З" U0417 # CYRILLIC CAPITAL LETTER ZE <Multi_key> <e> <3> : "з" U0437 # CYRILLIC SMALL LETTER ZE <Multi_key> <E> <3> : "З" U0417 # CYRILLIC CAPITAL LETTER ZE <Multi_key> <less> <3> : "❤️" U2764 # RED HEART <Multi_key> <s> <f> : "🌻" U1F33B # SUNFLOWER EMOJI Resources Compose Key cheat sheet Xorg/Keyboard configuration - ArchWiki