[brianogilvie]

It should be possible to do this (I don't remember the German equivalents of these commands, though). Quit OmniFocus and then:

1. In the Finder, select the OmniFocus application.

2. Choose Get Info.

3. Click the "Languages" triangle to reveal a checklist of languages.

4. Unselect everything except English. (Depending on your language preferences, it might suffice to unselect Deutsch, if English is your second preferred language.)

When you restart OmniFocus it will use English.