In German we simply add an s for the genitive, and we add an apostrophe when a letter is missing.
For example Jacob's book would be "Jakobs Buch" ¹ but John's book would be "Johannes' Buch", not "Johannes's Buch" ² and also not "Johannes'' Buch" ³.
¹ not "Jakob's Buch", which is called the "Deppenapostroph" - fool's apostrophe
² fool's apostrophe
³ fool's apostrophe and a second apostrophe to mark the cancelled letter
The genitive is nice, convenient and useful, yes. But there's no reason to add an apostrophe when no letter is missing.
(And as explained above, no, it is not foreign, this isn't changing anything in spoken language either, it's just a common spelling error due to commonly seeing it in English)
To draw a comparison regarding how annoying it is for anyone who cares about written language: It's quite similar to as if people in English suddenly started marking the plural with an apostrophe. Or if "would of" instead of "would have" would become correct.
So if many people (still a minority by a large margin of course) started writing things like "I would of visited the museum's today but I saw two rare bird's, their just so fascinating." it should become correct?
It's not like a majority is using apostrophes for the genitive in German. But since it's so easy to spot the few % of miswritten genitives just stand out.