Hi Alberto,

Launch Windows Live Mail and follow these steps:
1. Click the blue button.
2. Click Options and click Mail as shown in the image.
3. Click the Spelling tab.
4. Select the Language you would like and click Install if it is not installed already.
5. Select the installed language and click Set Default.
6. Click Apply and OK as shown in the image.
Note: Once the language is set as default. It will appear in bold letters.

Hope this helps.
Please revert for any clarification.

Thanks and Regards,
Manpreet C