More "English (UK)" Google quirks

Today I found myself giving instruction to a young whippersnapper on the basics of using Google Chat. I was very impressed when my pupil started sending me a whole string of increasingly intricate smilies. When I enquired how they might know so many smilie shortcuts they told me they were clicking on the "blue smilie face, to the right of the 'Pop-out' text". Needless to say, one of these I did not have.

I remembered that Google Chat was initially only available when the Gmail language setting was "English (US)". With my language option set to "English (UK)" the Chat functionality simply did not appear. But this was fixed months and months ago.

Sure enough, reverting my settings to US caused me to gain the missing icon. I'm now left with two questions.

1) What benefit does the Gmail "English (UK)" display language option give me?

2) Why is there any functional difference between "English (US)" and "English (UK)" anyway?

Now that I'm using "English (US)" once more I see the mysterious "Older version" option that does not appear under the UK variant. I wonder what that does...