Open Sans - Latin Extended Subset

Hi,

My issue is probably quite rare and not very serious, but I would like to optimize it nevertheless.

Not counting a few FontAwesome icons, I only use Open Sans on the site.
I set up Open Sans everywhere in Typography Options.
I thought everything was fine, until I tested the site in MS Edge.
I frequently use non-English characters, such as Č, Ř, Ě - and Edge inserted these letters from some funky font instead of Open Sans, which looked quite bad. Opera/Firefox don't have this issue.

So, here is what I did: In GP Hooks I imported this to the head:

<link href="https://fonts.googleapis.com/css?family=Open+Sans:400,400i,600,700,800&subset=latin-ext" rel="stylesheet">

And it works, Edge displays the pages correctly, but as far as I can tell Open Sans is loaded twice. Once the regular set, and then Latin-Extended.

Google PageSpeed Insights tell me:

Optimize CSS Delivery of:

https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,regular,italic,600,600italic,700,700italic,800,800italic%7COpen+Sans:400,400i,600,700,800&subset=latin-ext

which shows that

Open+Sans:300,300italic,regular,italic,600,600italic,700,700italic,800,800italic

from the regular subset are being loaded. My site doesn't need them, when I import 400,600,700,800 from the Latin Extended subset.

Perhaps, there is some trick:
a) to make GP load Open Sans-Latin Extended or
b) to make GP not to load Open Sans at all, because it is imported via GP Hooks

Or perhaps there is a better way?

I would like to make the site as fast as possible and avoid unnecessary file requests.

Cheers
Tom