I don’t have help, looks like you got some that might work for you. I do have a couple of observations. The xls2csv is not using ReadData. Perhaps you should manually read.

There is no such thing as high ASCII. It’s ASCII or not and ASCII has no support for diacritics. So you’re almost certainly working with Latin-1, CP-1252, UTF-8, or perhaps should be trying to use UTF-16LE as 1nickt suggests.

All that stuff about “plain text = ascii = characters are 8 bits” is not only wrong, it’s hopelessly wrong, and if you’re still programming that way, you’re not much better than a medical doctor who doesn’t believe in germs. Please do not write another line of code until you finish reading this article. –The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)