Greek

The standard modern Greek keyboard layout

The key ";:" has the functionality of a dead key; you press it (nothing is printed) and then you press a vowel, and the vowel appears with a TONOS accent mark (άέήίύόώ). When you press ":" and then either IOTA (ι) or YPSILON (υ), these letters get the DIALYTIKA accent mark (ΐ ΰ).

` 1 2 3 4 5 6 7 8 9 0 - =
   ; ς ε ρ τ υ θ ι ο π [ ] \
    α σ δ φ γ η ξ κ λ ´ '
     ζ χ ψ ω β ν μ , . /

~ ! @ # $ % & * ( ) _ +
   : Σ Ε Ρ Τ Υ Θ Ι Ο Π { } |
    Α Σ Δ Φ Γ Η Ξ Κ Λ "" 
     Ζ Χ Ψ Ω Β Ν Μ < > ?

There is a keyboard layout to type Classical Polytonic Greek. There is a bug report with this issue and GTK+ applications, described at GNOME Bugzilla #321896. See general instructions (in Greek) with screenshots from FC2.