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Are you sure Google Fonts aren't blocked or something? I believe this theme uses Open Sans font from Google Fonts. Anyway, "~" looks fine here.
screenshot-by-nimbus.jpeg 46.12KB 1 downloads
Although I dunno if you actually didn't like how this font display that character. I mean, I personally think that this font's "~" doesn't differ much with that font's (the one you used as example). Thus, it made me doubt that you were actually on the same font as me.
Edited by Bobby W., 20 September 2014 - 02:36 PM.