I would like to produce several PDF and SVG files out of SVG template with several text variables (name, address, etc.) filled in from database (could be just text CSV file).
The only solution I found is an article in Russian how to do it with php script:
http://diomer.ru/read/create-pdf-with-p ... om-patter/
But I would like to do it within Inkscape (+extentions).

Is it a build-in possibility or an extension for that? I could not find...

The quickest way is probably to write a short command line script, using sed - SVG files are just text, you can batch edit them easily via command line.
Then you can use Inkscape command line interface to export to pdf.

As far as I know, there is no extension yet that does that (but I don't think it would be too hard to make one, as the building blocks - like reading a CSV file, exporting to pdf, search+replace - are all available in other extensions already).

Well, what it sounds like you want to do is over my head. But I just came across this extension which is said to take text from a CSV file and put in Inkscape canvas: viewtopic.php?f=11&t=9212

Maybe will do part of your project?