You might take a look at
this section of NeoOffice's wiki page on Spellcheck. It provides some suggested ways to quickly change languages in a document, so the spellchecker will work correctly. (Since it is written for NeoOffice, OOo users will need to keep in mind that the command key on a Mac=the control key on Windows and Linux. Also a control-click is the same thing as a right click. I'm not sure whether those changes apply to OOo/X11 for Mac).
That may not be all you are after, though. I work in NeoOffice (a Mac port/fork of OOo), and to switch between English and Hebrew I also have to change the MacOSX input method I use. (That's not necessary for switching between English and French, though, unless one prefers the French keyboard).
kabing
Edit: clarified my description of the article
NeoOffice (app store version) OpenOffice.org 4.1 and LibreOffice 4.3 on Mac OS X El Capitan
OpenOffice.org 4.1.2 on Windows 10 (Previously on Vista)