I have a data collection application from facebook, it worked very well a few days ago. Currently,it's work, but cannot get the locale field to classify data. I use Graph API:
https://graph.facebook.com/v2.6/<user_id>?fields=first_name,locale&access_token= <access_token>
Is there any way to solve this problem?
Not only locale is deprecated for today. More information you can check here https://developers.facebook.com/blog/post/2018/05/01/facebook-login-updates-further-protect-privacy/
If you are using web canvas app, you can get current user locale from POST request, which facebook platform do each time when your app started. So you can find 2 fields: signed_request, fb_locale. It works only for current user but still. Maybe this information will be usefull.
If you have mobile app or something else you should try investigate this trick. It works for me.