Use getHtmlCode() instead of getCode() to set the lang attribute

The lang attribute of HTML elements should conform to BCP 47.

Change-Id: Ia8a088add29daea39e90bb277279a6485990d18a
Escape message 'word-separator' on Special:FileDuplicateSearch

Change-Id: Ib00cbca264d5723434e5db476293364267a13a85
Merge "Escape message 'word-separator' on Special:FileDuplicateSearch"
Merge "Use getHtmlCode() instead of getCode() to set the lang attribute"