Update i18n system

What I did in this patch:

Added the new strings to interface_localization.js
Inserted the mandatory span tags required by Polyglot to recognize strings for translation.
Wrote JavaScript required to localize placeholders, labels and tooltips.
Applied Polyglot to a few strings where it was missing.
Fixed support for special unicode characters in theme-nin.

I also used it to make one new localization (Czech).
No - if you look at the code, this text (with this exact key) already exists in English, and has already been translated into several languages, but the UI wasn't using it, so I fixed that.