[telotortium]

This is the first time I've ever seen this construction (using "that's" instead of "whose" as a relative possessive pronoun): "...the ongoing use of English, a language that's reach and influence has grown considerably..."

[Stratoscope]

That's not very typical. (Pun intended, and John Clarke reference intended too.)

It was just a mistake. Given the topic, it's possible that that was written by someone who's not a native speaker - but whose writing is otherwise very good. (And arguably better than that showoff sentence!)

As you noted, a native American English speaker would write "...a language whose reach..." And that's that.

RIP John Clarke:

https://www.youtube.com/watch?v=3m5qxZm_JqM

[megaman22]

Contractions in vernacular American English are such a shitshow and getting worse all the time, that I'm not sure any guardians of proper usage can stand against the tide.