There seems to be an issue with a file that has been corrupted or otherwise uploaded incorrectly.
http://matchhistory.na.leagueoflegends.com/assets/1.0.0/codex/codex/util/I18n.js
Unless it's a local issue, which I doubt, loading up the same file from a different regions server shows how it should look.
http://matchhistory.oce.leagueoflegends.com/assets/1.0.0/codex/codex/util/I18n.js
I might be mistaken, but I've tried a few different methods to pull the file. I've saved the entire page via firefox, internet explorer, pulled the source up via link (as here) and even pulled the file using external downloaders. Every time the file is cut short, at least for me at:
"Damage Taken & Healed","breakdown_hea