I believe that the storage format is tokenised, and the editor translates back and forth between token number and local language keywords, so that code can work on different systems. But I don't know for sure - my experience with MS Office is very minimal (the last version I had on my own systems was Word for Windows 2, on Win 3.11. I use LaTeX when I can, LibreOffice otherwise).
Excel does the same thing - function names are different in different languages, and are a real pain to deal with. You can't copy and paste easily, you can't look at examples on a web page in a different language and expect them to work. You can't even get the idiotic thing to import or export text formats if the file's idea of decimal comma vs. decimal point differs from your Window's setup. It might be workable for people who work solely in a single non-English language and don't understand English, but it is annoying for mixed language usage. MS really should look at LibreOffice to learn how office software should work.