locales of files from other users

Hello,
I have a file (I converted it from .xlsx to .gnumeric) that was sent to
me by another person; they almost certainly use a locale where numbers
have a comma as decimal separator. 

No matter what locale variables I set, ssconvert always generates
csv/txt files with commas in numbers. Is that because of the locale of
the original author? Do I understand the locale issue correctly?

Can I force my locale on ssconvert output?

All the Best,
Andrei