locale for facebook like button

TheCrow: not sure I understood your question. if language is not set, the way it is now, FB button code detects the browser or system language automatically and shows the button in this language.

but this creates theming problems: "like" has 4 letters (best button width 90px), in other languages equivalents can be 3-15 letters (up to 150px button width).
the width of button is set explicitly now and doesn't depend on the length of the used word. there's inconsistency in looks: wide margins or clipping. so some themers would prefer to set language explicitly too if their site uses only one language.

localisation project is used mostly for the sites with 2 or more languages used. this sites would probably prefer to leave &locale= blank for FB to autodetect and just set very big button width to avoid clipping. other solutions would be rather complicated

I checked the patch, and it works, but the $vars['subst']['locale'] = strtolower($vars['subst']['locale']) . '_' . strtoupper($vars['subst']['locale']); looks wrong.
why not simply allow input of normal 5-letter locale like es_AR, es_BR, pt_BR, pt_PT, en_EN, en_US etc.?
btw not every locale has first 2 letters equal to last 2 letters...

tested, works
as this is a rather simple patch, I suggest commiting it without further reviewing
thank you