"20.000" means "20 + 0/1000" in English, "20000" in some European languages. "20,000" is Polish for "20 + 0/1000", the same might be in other European languages. It might also mean "20 and 000" as two numbers. (I haven't checked how many packages there really are.)
https://en.wikipedia.org/wiki/Decimal_mark#Digit_grouping suggests thin spaces being more portable (they are   in HTML). The package containing this text is ubiquity-slideshow-trisquel in trisquel-packages.git, it's not a modified Ubuntu package (using a helper). The file is at [0]. [0] http://devel.trisquel.info/gitweb/?p=trisquel-packages.git;a=blob;f=extra/ubiquity-slideshow-trisquel/data/usr/share/ubiquity-slideshow/slides/welcome.html;h=8b0c6acff602f91344b478d389d34105f3fb25b2;hb=HEAD
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