I wrote about this before hitanykey.webs.com/mar142012.html , but Facebook keeps changing things. So until they change it again, here's an update.
I just had a computer bought to me, a Windows 7 laptop, the owner said that the language on her computer had changed. She mentioned she was on Facebook when it happened. So I turned it on but everything seemed normal so I opened her browser and went into her Facebook account and it was changed to what I discovered was Portuguese. The hardest part is knowing where to click to fix things right.
I'm assuming here you can't read the language enough to get it set back.
If your using Chrome you probably will have no problem if Chrome gives you the option to translate it. Otherwise do the following.
Sign Into Your Account As Normal
Go Into Your Account Settings. That is the little upside down triangle and when the menu drops down the menu is divided up into five sections with gray lines. The settings option is in the fourth section, third item down.
Click on the Language symbol, use to be a blue ball, under the red ball with a white dash in it. It's now a square shape, blue in colour, with a white letter A and another symbol I can't make out.
Then in the first line click on the Edit option, whatever language it is in.
Then you get an option to choose your language in the drop down menu.
Finally click on the blue button that in English says Save Changes. It should work immediately.
I had to fix this problem before for someone else. How this happens? I can only assume that this happens when you click on a link to download an app and it changes the system settings.
I realize some languages may radically change the way the page looks. Some languages are read from right to left for example. I found another way to change the language if the previous method doesn't work.
Sign in, across the top blue bar click on your Name.
Scroll down the left hand side of the page, in my case, and look for a rectangular shaped box with a plus sign in a square box or something similar.
Click on that plus sign and in the window that opens chose your language.
Use the Status bar
When you place your mouse cursor over a link you’ll notice the link info will appear at the very bottom of your browser window. I’ve changed my Facebook page to French on purpose and I noticed this status bar info is still displayed in English. You might be able to use this to navigate around.
If all else fails go to https://www.facebook.com/help/ . You might be able to find some support there.