Why does typing two commas not convert into German opening quotation marks?

Question

I read in another question that it is possible to use the shorthand of typing two commas, which should then compile into opening German quotation marks. Here is a minimal working example:

\documentclass[a4paper,ngerman]{scrartcl}
\usepackage[ngerman]{babel}
\begin{document}
Dies ist ein ,,Test``.
Dies ist ein anderer \glqq Test\grqq{}.
\end{document}

I noticed that when compiling with PDFLaTeX, the output looks as follows (note that only the double acutes are compiled correctly, probably because they are the shorthand for both German closing and English opening quotation marks):

Compiling with XeLaTeX or LuaLaTeX, both shorthands are detected properly:

It seems like PDFLaTeX does not contain the shorthand definition for quotation marks other than the English ones. Is there a way of using the shorthands for other languages with PDFLaTeX, e.g. by installing an additional package?

Answer 1

For languages where diacritics are used it's recommended to add

\usepackage[T1]{fontenc}

when using pdflatex, so the letters with the diacritics will be precomposed and will work properly in hyphenation.

The default font encoding is OT1, where no ligature for ,, is usually defined, for the simple reason that (most of) the OT1-encoded fonts don't have low German quotes to begin with.

To the contrary, T1-encoded fonts have (or should have) a ligature for ,, and suitable kerning pairs.

\documentclass[a4paper,ngerman]{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\begin{document}
Dies ist ein ,,Test``.
Dies ist ein anderer \glqq Test\grqq{}.
\end{document}