Update header.tpl

[MindaugasR]

Added that Open Sans support UTF-8:

Source: http://stackoverflow.com/questions/4495098/google-fonts-css-latin-question

[DamienMetzger]

Hello,

Thus do you want to fix this pull request or just close it?

Thank you,

[DamienMetzger]

Hello,

It's a trade off between weight and compatibility.
http://www.google.com/fonts#UsePlace:use/Collection:Open+Sans
Try checking the extended charset and see to weight increase.

We need to implement a feature that loads the correct charset according to the language.

[MindaugasR]

Everything works fine for me with 300,600 weights. So I think, just need to add this:
&subset=latin,latin-ext
For correct charset.