Q: Screen connect 2 iMacs (late 2009) with mini DisplayPort

Only press command-F2 on the iMac that you want to act as a display.

At a minimum, you would need the two keyboards anytime that you restart the iMac acting as a display.

Use your iMac as a display with Target Display Mode - Apple Support

Impressions63 wrote:

 

...

When I press Cntrl F2 on the left, ...

You should be pressing command-F2 not control-F2.

Have you tried the items mentioned in that article?

• In Keyboard System Preferences, if the checkbox is enabled for Use all F1, F2, etc. keys as standard functions keys, the key combination changes to Command-Fn-F2.
• Make sure your Mini DisplayPort or Thunderbolt cable is connected to both computers.
• If you're currently logged in on the iMac you want to use as a display, try logging out to return to the login window. Then press Command-F2 again.
• Some older Apple keyboards and third-party keyboards might not allow Command-F2 to toggle display modes. If this happens, use the keyboard that came with your iMac to toggle Target Display Mode on and off.

After enabling the display via command-F2 have you tried opening System Preferences -> Displays on the other iMac? You should be able to arrange the monitors to the correct orientation. OS X: How to use multiple displays with your Mac in Mountain Lion and earlier - Apple Support

In the System Preferences -> Displays -> Arrangement drag the menu bar to the display that you want to act as the main display.

Being non-english and upside down it is impossible to read.

Take a look at the article I provided the link to earlier. In your screen shot, I believe that you need to click the middle button in the preference pane on the right side iMac.