Why would you want to use sed when the Perl regexes are far far far more powerful?

If you feel limited in your command of Perl regexes, I really think that the first thing you want to do is to really start mastering the Perl regexes. Perhaps reading Mastering Regular Expressions, by Jeff Friedl. BTW, this book also shows some of the limitations of regexes, and you project will necessarily meet these limitations. I think that most people on this forum agree that you should not use regexes for parsing HTML or XML, using regexes for parsing PHP would be even worse.

Although regexes might certainly do part of the work, I doubt that you can go anywhere without using a real parser.

One final note on the English-Russian translation anecdote, I personally tried several translating software packages over the years (I was a translator before I became a CS professional) between 1988 and 1996. The results were really bad. On the first one I tried, i gave the following sentence: "Time flies like an arrow". The French translation I obtained was: "Les mouches du temps aiment une flèche", which can be translated back into English as follows: "The flies (the insect) of time love an arrow". I tried other packages at the time, the results were possibly not as funny, but not much better. A lot of improvements have been made since, but the basic problem of implicit context understanding is still there.