A Postscript file is just a description of the appearance of a page, whether that page has words or pictures, like a PDF file. The expensive printers used by businesses can all print a Postscript file, so Linux programs generally produce one when asked to print. If you have a document in UTF-8 or any other coding, and you ask a program to print it, that program converts each page to a Postscript file.
Ghostscript started as a tool to let people see what's inside a Postscript file, by converting it into a bitmap to display on the screen. When they started making cheap printers that worked in graphics mode instead of having fonts, it was obvious that you could use Ghostscript to produce a bitmap to send to the printer as well as one to send to a screen. The PPD file just has information about the printer so that Ghostscript knows what to do.
The important thing is that none of these programs deal with characters or languages. The characters are in the word-processor document, not in the files used by the printing system: they just contain graphical images, like the one you see on your screen. Remember, when you see an "a" on the screen you are actually looking at a pattern of pixels, and that's what the printer gets as well. Only the word-processor needs to know what alphabet you're using.