I found a thread in which the following Applescript was contained:
tell application "System Events" to set p to (path to frontmost application) as string
tell application "System Preferences"
activate
reveal anchor "Dictation" of pane "com.apple.preference.speech"
end tell
tell application "System Events"
tell process "System Preferences"
tell pop up button 1 of tab group 1 of window "Dictation & Speech"
click
if (get value of attribute "AXValue") contains "English (United States)" then
click menu item "German" of menu 1
say "Dictation set to German"
else if (get value of attribute "AXValue") contains "German" then
click menu item "English (United States)" of menu 1
say "Dictation set to English"
end if
end tell
end tell
end tell
quit application "System Preferences"
activate application p
I tested it out and it works. All you have to do is change "German" to the language of your choice.
Additionally, may I suggest an application called FastScripts, which allows you to run the applescript either from the top menu bar or from a keyboard shortcut.
Hope this solved your problem!