Omnipotent compose key

Two keyboard layouts are all you need. I have a Cyrillic and a Latin one. So I can type in Russian and many-many other languages including Estonian. For the later one, I use the omnipotent compose key. The compose key is a key to trigger the insertion of a precomposed character. Shortly, it allows me to type “äöüõ”. Moreover, it simplifies typing “š” in my family name (Ivaništšev). Believe me, this is more difficult with the Estonian layout. Also, I can type “€” sign.

On Linux (Gnome) you can activate it as: System > Preferences > Keyboard > Layouts > Layout Options > Compose key. Choose the preferred button that will turn on the composition mode. I prefer Caps Lock. On Windows one requires special software. For example, wincompose.

The life seems so beautiful when everything is set, and the UK layout is set to default.

Besides, one can enable compose for Greek alphabet by adding to ~/.XCompose file:

# GREEK CAPITAL LETTERS
<Multi_key> <G> <A> : "Α" U0391 # GREEK CAPITAL LETTER ALPHA
<Multi_key> <G> <B> : "Β" U0392 # GREEK CAPITAL LETTER BETA
<Multi_key> <G> <G> : "Γ" U0393 # GREEK CAPITAL LETTER GAMMA
<Multi_key> <G> <D> : "Δ" U0394 # GREEK CAPITAL LETTER DELTA
<Multi_key> <G> <E> : "Ε" U0395 # GREEK CAPITAL LETTER EPSILON
<Multi_key> <G> <Z> : "Ζ" U0396 # GREEK CAPITAL LETTER ZETA
<Multi_key> <G> <H> : "Η" U0397 # GREEK CAPITAL LETTER ETA
<Multi_key> <G> <I> : "Ι" U0399 # GREEK CAPITAL LETTER IOTA
<Multi_key> <G> <K> : "Κ" U039A # GREEK CAPITAL LETTER KAPPA
<Multi_key> <G> <L> : "Λ" U039B # GREEK CAPITAL LETTER LAMDA
<Multi_key> <G> <M> : "Μ" U039C # GREEK CAPITAL LETTER MU
<Multi_key> <G> <N> : "Ν" U039D # GREEK CAPITAL LETTER NU
<Multi_key> <G> <P> : "Π" U03A0 # GREEK CAPITAL LETTER PI
<Multi_key> <G> <R> : "Ρ" U03A1 # GREEK CAPITAL LETTER RHO
<Multi_key> <G> <S> : "Σ" U03A3 # GREEK CAPITAL LETTER SIGMA
<Multi_key> <G> <T> : "Τ" U03A4 # GREEK CAPITAL LETTER TAU
<Multi_key> <G> <U> : "Υ" U03A5 # GREEK CAPITAL LETTER UPSILON
<Multi_key> <G> <F> : "Φ" U03A6 # GREEK CAPITAL LETTER PHI
<Multi_key> <G> <X> : "Χ" U03A7 # GREEK CAPITAL LETTER CHI
<Multi_key> <G> <W> : "Ω" U03A9 # GREEK CAPITAL LETTER OMEGA
<Multi_key> <G> <O> : "Θ" U0398 # GREEK CAPITAL LETTER THETA
<Multi_key> <G> <Y> : "Ψ" U03A8 # GREEK CAPITAL LETTER PSI
<Multi_key> <G> <C> : "Ξ" U039E # GREEK CAPITAL LETTER XI

# greek small letters
<Multi_key> <g> <a> : "α" U03B1 # GREEK SMALL LETTER ALPHA
<Multi_key> <g> <b> : "β" U03B2 # GREEK SMALL LETTER BETA
<Multi_key> <g> <g> : "γ" U03B3 # GREEK SMALL LETTER GAMMA
<Multi_key> <g> <d> : "δ" U03B4 # GREEK SMALL LETTER DELTA
<Multi_key> <g> <e> : "ε" U03B5 # GREEK SMALL LETTER EPSILON
<Multi_key> <g> <z> : "ζ" U03B6 # GREEK SMALL LETTER ZETA
<Multi_key> <g> <h> : "η" U03B7 # GREEK SMALL LETTER ETA
<Multi_key> <g> <i> : "ι" U03B9 # GREEK SMALL LETTER IOTA
<Multi_key> <g> <k> : "κ" U03BA # GREEK SMALL LETTER KAPPA
<Multi_key> <g> <l> : "λ" U03BB # GREEK SMALL LETTER LAMDA
<Multi_key> <g> <m> : "μ" U03BC # GREEK SMALL LETTER MU
<Multi_key> <g> <n> : "ν" U03BD # GREEK SMALL LETTER NU
<Multi_key> <g> <p> : "π" U03C0 # GREEK SMALL LETTER PI
<Multi_key> <g> <r> : "ρ" U03C1 # GREEK SMALL LETTER RHO
<Multi_key> <g> <s> : "σ" U03C3 # GREEK SMALL LETTER SIGMA
<Multi_key> <g> <t> : "τ" U03C4 # GREEK SMALL LETTER TAU
<Multi_key> <g> <u> : "υ" U03C5 # GREEK SMALL LETTER UPSILON
<Multi_key> <g> <f> : "φ" U03C6 # GREEK SMALL LETTER PHI
<Multi_key> <g> <x> : "χ" U03C7 # GREEK SMALL LETTER CHI
<Multi_key> <g> <w> : "ω" U03C9 # GREEK SMALL LETTER OMEGA
<Multi_key> <g> <t> : "o" U03B8 # GREEK SMALL LETTER THETA
<Multi_key> <g> <y> : "ψ" U03C8 # GREEK SMALL LETTER PSI
<Multi_key> <g> <c> : "ξ" U03BE # GREEK SMALL LETTER XI

# special characters
<Multi_key> <minus> <minus> <minus>     : "−" U2212 # MINUS
<Multi_key> <minus> <minus> <greater>   : "→" U2191 # RIGHTWARDS ARROW
<Multi_key> <minus> <minus> <less>      : "←" U2193 # LEFTWARDS ARROW
<Multi_key> <minus> <greater> <greater> : "↑" U2191 # UPWARDS ARROW
<Multi_key> <minus> <less> <less>       : "↓" U2193 # DOWNWARDS ARROW
<Multi_key> <minus> <less> <greater>    : "⇌" U21cc # EQUILIBRIUM ARROW
<Multi_key> <minus> <greater> <less>    : "⇄" U21c4 # BACKFORWARD ARROW

P.S. a useful link https://tuttle.github.io/python-useful/compose-key-cheat-sheet.html
P.P.S. the missing signs can be inserted as Ctrl+Shift+U+XXXX+Enter, 2212 for −, 21cc for ⇌, 21c4 for ⇄, 2191 for ↑, 2193 for ↓.