Add German umlauts and currency signs to current key map

.Xmodmap-AddUmlauts

!
! Add German diaereses (Umlauts) and some currency signs to current keymap 
! as <AltGr> alternatives to related English letter keys, e.g.
! 
!     <AltGr>-<A>          =  ä
!     <AltGr>-<Shift>-<A>  =  Ä
!
! Load with "xmodmap .Xmodmap-AddUmlauts"
!
! ----------------------------------------------------------------
! NOTE:
!
! ONLY works with some keyboard layouts, like "gb" or "us(altgr-intl)".
!
! Layouts that do not map <AltGr> (usually keycode 92 or 108) to 
! ISO_Level3_Shift but e.g. ALT_R can't work, e.g. "us".
!
! For yet unknown reason, even some layouts that do map <AltGr>  to
! ISO_Level3_Shift do not work, e.g. "us(alt-intl)"
! ----------------------------------------------------------------
!
keycode  26 = e E e E EuroSign   EuroSign
keycode  30 = u U u U udiaeresis Udiaeresis
keycode  32 = o O o O odiaeresis Odiaeresis
keycode  38 = a A a A adiaeresis Adiaeresis
keycode  39 = s S s S ssharp     section
keycode  46 = l L l L sterling   sterling

Another way that integrates better with Unity/Gnome: https://gist.github.com/nilstoedtmann/e9de2394194a6c8381a4daaf13b79919