This is going to take some heavy duty trouble shooting. Your going to need to use a program like
Winmerge to compare all your files to a good copy to find out where the mistake is. The difficulty of this method will varry depending on the mod's you have installed.
Another thing to keep in mind is that you need to use a proper file editing program such as
Notepad++ that will save the files in the same encoding they came in, in this case, UTF-8 w/o BOM. Notepad++ will even work with a lot of the popular FTP programs (like CrossFTP) so when you hit Edit in the FTP program, it opens notepad, then saving in Notepad++ automatically uploads the file.
If you have already edited any of your language files using the regular windows notepad.exe or any other program that cannot save in UTF-8 Without BOM, what you need to do is download, install and run notepad++ (or edit from ftp into notepad++), either way, when editing the file, in the menu up top, hit format, then chose "Convert to UTF-8 Without BOM" and then save and re-upload if needed.
God luck, you'll need it.
Typo