Hi
Please see extract from Office Support page:
Set the default editing language in Office 2010

1. Open a Microsoft Office program, such as Word.
2. Click the File tab.
3. Click Word Options.
4. Click Language.
5. In the Set the Office Language Preferences dialog box, under Choose Editing Languages, select the editing language that you want to use, click the name of the language that you want to be the default language, click Set as Default.
6. After you change the default editing language, you need to close all your Office 2010 programs, and then open them again for the change to take effect.

Notes

• If for some reason, your default display or Help language is not available, Microsoft Office uses the next language in the list that is available.
• If the language that you want is not listed, you might need to add more language services by clicking Add additional Editing Languages.

Good luck.
Tony (OTPM)