Well I would still guess that the file is not actually utf-8, and believe it more since when you “converted” it to utf-8 it came out wrong: you have to know the original encoding (and open the file in that encoding) before you can correctly convert it. What format did the online converter convert from? And changing the settings in the text editor won’t change the encoding of an individual file, it will change the format it writes to by default, I believe.
I haven’t used TextEdit for a long time, because it pulled some crap like this on me one time. If I remember correctly, Text Edit saves things by default as ‘rich text file’ (rtf) format, and makes it less than obvious to save as a more standard text file.
Knowing you use TextEdit, and knowing that it displays your text correctly, I would try these steps I found online to save as a more normal utf-8 text file from within TextEdit:
TextEdit (for Mac)
Go to 'Format' and select 'Make Plain Text'.
Click 'File' and choose 'Save...'.
From the 'Plain Text Encoding' dropdown choose 'Unicode (UTF-8)'.
Click 'Save'.
I would then open that file in a different (better 
) editor and copy from there. I like sublime text editor, I’ve seen others using Atom, seemed cool. Let us know if this works!