For example, I could be reading something posted by a Frenchman, with very bad english, just enough to communicate his problem. It's obvious he'll have great problems dealing with http://www.php.net/manual/en/ref.regex.php, but what if he wants to read that in French? Sure, he could click on the language selection thinger at the top, but in all fairness, it's his time and bandwidth being used up, as well as that of the php.net mirror.
Oh, and don't forget about Boris the Russian, Jan the Sapiard and Jurgen the Generalised European.
Why not just use http://www.php.net/regex? It's clean, simple, and it automatically detects your language settings.
Just a suggestion, but I think you'll agree it could be helpful