This entire topic is obsolete now, as autorevision will demand svn to use XML output in the future (the downside is that you will no longer be able to use Subversion 1.2 or 1.1).
However, even before that, it should not matter what languages you or anybody else have installed ony our system. Nobody wants to know. Nobody wants to use them, it has to work anyway.
The issues that existed with autorevision are the very fact that people have certain localisations on their system, for example German or French. That means that Subversion will output something like "Letztes Änderungsdatum" or "Date de la dernière modifciation" or some other bullshit which is impossible to parse. There was no way to get an output that you could parse in a reliable way.
I even intended to use something like "jfwlyidlkjfg" as the locale setting, but Lieven changed it to "en_US" due to demand by a few people who saw errors/warnings (not all systems handle the fallback alike :?).
Any setting is OK as long as it defaults to the language that is built into the Subversion executable, not some arbitrary localisation (an invalid localisation normally defaults to the string built into the executable, but some systems emit a warning). en_US is what seems to be Subversion's builtin language, so that is what was chosen.
