I got the same issue…
The problem is not really your script but Google broken pseudo-xml-html-text like format… which is locale & language dependant…
<content type='html'>Date : ven. 16 oct. 2015 20:00 au 22:00
CEST
<link rel='alternate' type='text/html' href='https://www.google.com/calendar/event?eid=...' title='alternate'/><link rel='self' type='application/atom+xml' href='https://www.google.com/calendar/feeds/.../public/basic/...'/><author><name>F...</name><email>f...</email></author></entry><entry><id>https://www.google.com/calendar/feeds/.../public/basic/...</id><published>2014-10-21T08:02:16.000Z</published><updated>2014-10-21T08:02:43.000Z</updated><category scheme='https://schemas.google.com/g/2005#kind' term='https://schemas.google.com/g/2005#event'/><title type='html'>Sortie</title><summary type='html'>Date : sam. 14 mars 2015 08:00 au 17:00?
CET<br>
<br>état de l'événement : confirmé</summary>
I’ve noticed that the plugin then need to fetch a language dependant text, but even the date is locale dependant… except switch to ICS support (which would be a lot of work) I don’t see a solution. I’ll keep on using the integrated iframe from the big Google.