There is a compose functionality out there:

Linux umlaut typing

For the Gnome Desktop:

• go to System -> Preferences -> Hardware -> Keyboard on the Gnome menu
• select the Layouts tab
• click the Options… button
• expand Compose key position
• check the box Right Ctrl is Compose or Right Win-key is Compose

The Right Ctrl or the Right Win key are now a “compose key”. With it you can compose symbols by combining two characters. The double-quote then the letter “a” equals an umlaut-a (ä). Tap the compose key, then tap shift+quote for a double-quote, then tap the a-key.

• ä is compose, then “, then a
• ö is compose, then “, then o
• ü is compose, then “, then u
• ß is compose, then s, then s

The list of compose key sequences can be found at:

Compose key sequences

Content found at blog: http://idolinux.blogspot.com/

Kül