I still don't get it.
You can not convert utf8 to ASCII - other than the first 127 characters.
What you want is to represent the non-ASCII characters with some representation of the character that can be done with ASCII characters, making them readable.
Like f.ex. å in danish can be represented by aa.
Seems like the way to go then, would be a table lookup, for the individual characters.
There is 1,112,064 utf8 characters, and you would probably have to create the table yourself.
Still only one tenth of having to correct all the lines manually...
Could maybe be simplified by reading the string as bytes...