[site:url] is inconsistent depending on whether a language prefix is present

[site:url] may be used by itself in order to show a link to the site, or it may be concatenated with a string to produce a link to some resource like
[site:url]foo/bar.png
This usually results in something like
http://example.com/foo/bar.png
except if a language prefix is present, then for Spanish you get
http://example.com/esfoo/bar.png

[site:url] should always append a slash to make the output consistent.

The only downside is that a stand-alone link with a language prefix then becomes
http://example.com/es/
Which isn't really a problem - it's just not as aesthetically pleasing.