One of the greatest (in the sarcastic meaning of the word) work of localisation is Excel translating function names. So =SUM() is =SUMME() in German. Luckily opening the file works in different languages.
So if you mail a Dutch person a CSV file that follows RFC 4180, chances are they can't open it properly because of Excel. A surprisingly large number of otherwise capable people get stuck at this point.
(OpenOffice/LibreOffice is smart enough to recognise tabulated data when it sees it, and will simply present you with the import screen for tabulated data with its helpful live preview of the columns.)
So when I had to use Excel all the formulas were named in Norwegian.
I downloaded a portable version of LibreOffice but that triggered the anti-virus :I
Sometimes I would use Google Docs instead but for company confidential information I obviously won't upload that data to Google so then I'm stuck with Excel. Even for non-critical data Google Docs might not be an option simply because you are working on the file together with someone else who is using Excel and constantly uploading and downloading the file would be annoying, as well as the risk of Google Docs not supporting 100% of the features of Excel leading to complicated spreadsheets getting mangled. (Same problem with using LibreOffice to work with someone using Microsoft Office.)