Translate Issue XML view header

The Issue XML view has the header:

<rss version="0.92">
<channel>
    <title>#esc($title)</title>
    <link>#esc($requestContext.baseUrl)</link>
    <description>This file is an XML representation of an issue</description>
    <language>en</language>

The description should be internationalised, however we will need to investigate its side-effects. Need to ensure it does not break RSS/XML standard and whether we need to change the language tag in the header as well.