I give up, too difficult.
I tried it with "open office calc" I was able to select unicode utf8, but when opening the file, the data were all mixed up, impossible to work.
I tried with my excel (version 2002 sp3), but there is no choice unicode utf8. I tried it without selecting it. Opening the data are accurate and perfectly stacked and easy to change. After I saved it there was some incompatibilities and, after importing, I had all the prices changed. It seems to me that the damage I've only had on prices. Now I'll correct them and then I'll give up.
Too difficult! In the future, maybe, you can put a procedure a little more easy and quick to change the quantity of products.
The system: "import -> load Directly from textarea and write this: product_code, product_quantity"
works well; but every time you have to remember all the codes of the products and if you make a mistake just on 1 character, the system creates a new product.
For now, every time I'll have to do updates I'll open the file of each product.
Thanks anyway, always very kind