This sounds like you either missed some edits or perhaps put one in the wrong spot. You need to compare your edited files against the folder titled "phpBB_3.0.5_modified_files", which can be found in the contrib folder, using Winmerge
or another compare/merge program.
When you recheck the edits, take your time and do it right, checking every single edit again, paying close attention to the placement of the code and that you didn't skip or misunderstand any of the steps.
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.
I hope one of these two things sets you straight. Chances are, it has to be one or the other.