Translation via CSV File and Excel

I tried to translate my german version of the game I am working on. The goal is to create an english version.  So the workflow was: export language file as .csv, import in Excel, make the changes and them save and reimport it so Visionaire again.

Surprise: it doesn`t work. As long as I export the language file and do not touch it, the reimport works fine. The moment I opened it in Excel, Visionaire dosn`´t import it any more - even if I didn`t change the file. Just to open the file in Excel is enough to destroy it for a reimport to Visionaire.  

Any thoughts how I can use Excel to make my translation and then still get a valid csv file that can be read by Visionaire to import the new language assets?

Best

J