Switching to a different language through Facebook’s General Account Settings page only changes the site's language and does not allow you to type in the new language. To type text on Facebook using a language not based on the Latin alphabet, you need to add that language to Windows. Use the "Add a Language" feature in the "Time and Language" section of the Change PC Settings utility to add the language; Windows then automatically adds a virtual keyboard with keys to match the letters of the new language’s alphabet.
Add a New Language
Point your cursor to the top right corner of the screen, and then select the "Settings" charm.
Select "Change PC Settings," and then select "Time and Language."
Select "Region and Language," and then select "Add a Language."
Scroll through the list of languages, and then select the language you want to use on Facebook.
Sign in to your Facebook account, and then click in the area where you want to type, such as the Update Status box.
Press the "Windows-Spacebar" keys to switch from English to the new language. Start typing in the new language.
Type With a Virtual Keyboard
Sign in to your Facebook account, and then press the "Windows-U" keys to open the "Ease of Access" window.
Click "Start On-Screen Keyboard" to launch the keyboard, and then press the "Windows-Spacebar" keys to switch to the new language’s keyboard.
Click in the area on Facebook where you want to type, such as a Comment box, and then type your message in the new language with the virtual keyboard.