Escape language strings for JS

[Destroy666x]

As I suggested under my lang commit, there should be some sort of support for languages which are often using apostophes (for example French) so that JS errors don't happen. Simply escaping them with Twig should be fine.

[JN-Jones]

There's only that "delete confirmation" dialog where this applies atm, isn't it? That one should be left for now as we'll likely use a modal/dialog instead of a js popup.
But generally, yes, this should be added for sure.

[ATofighi]

I think it is fixed in 260cf6c

[Destroy666x]

#159 seems to fix it indeed, at least the current lang strings.