OpenOffice.org 2.4 adds three new ways to select the language for easier use. Changing the language to indicate to the spell checker which dictionary to use becomes very easy and intuitive.
Right click on any misspelled word to bring up the context menu. Then, choose the language for the selection or for the paragraph. OpenOffice.org 2.4 Writer context menu for misspelled word allows you to change the text language. The language options in this menu are not shown unless the selected word is misspelled.
More info at OpenOffice.org Ninja.
