Hello. Thank you for contacting the Toolset support.
Are you using the above code? What if you try to change the hook priority to 20? Does that help? if no:
Can you please share where you added the login form as well as send me admin access details.
*** Please make a FULL BACKUP of your database and website.***
I would also eventually need to request temporary access (WP-Admin and FTP) to your site. Preferably to a test site where the problem has been replicated if possible in order to be of better help and check if some configurations might need to be changed.
I have set the next reply to private which means only you and I have access to it.
Yes I understand that, that's why I have to use this code with Toolset. Without Toolset, the login form, the password change emails and other stuff, are properly site's default language. (And not all/partly in English as always with Toolset.)
For some reason I don't now quite get my message through. Anyway, let's forget this, if this really is the way Toolset works: Toolset does not use core's translations concerning login.