How to set a global setting for hyphenation of already hyphenated words using XeLaTeX?

Question

Please consider the MWE below, I want to globally invoke hyphenation of already hyphenated words using Babel package, Hyphenat package in English, to get the same effect when using <word1>-\hspace{0pt}<word2> as shown in the output below.

This is hopefully to avoid tracking down every hyphenated word in a thesis last-minute scenario, especially after doing some text edit in a 200-page thesis. I am quite satisfied with the effect of \hspace{0pt}, and I don't see any reason against using it blindly, or am I missing something?

MWE Code

\documentclass{scrartcl} % complied with XeLaTeX
\usepackage[english]{babel}
%\defineshorthand{"-}{\babelhyphen{hard}} % didn't work
\usepackage{fontspec}
\usepackage{libertine}

\begin{document}
In summary, IL-17 can be produced by innate and adaptive cells, but more profoundly from innate sentinel cells of the immune system. 
The nTh17 is a novel subset that is thymic-\hspace{0pt}dependent and shows a distinct developmental pathway from iTh17 cells that are derived from naive T cells.

In summary, IL-17 can be produced by innate and adaptive cells, but more profoundly from innate sentinel cells of the immune system. 
The nTh17 is a novel subset that is thymic"-dependent and shows a distinct developmental pathway from iTh17 cells that are derived from naive T cells.
\end{document}

Output

Answer 1

You're forgetting to add the shorthands to the list of enabled shorthands:

\documentclass{scrartcl}
\usepackage[english]{babel}

\usepackage{fontspec}
\usepackage{libertine}

\useshorthands{"}
\defineshorthand[english]{"-}{\babelhyphen{hard}} % didn't work
\addto\extrasenglish{\languageshorthands{english}}

\begin{document}

\makeatletter
\show"

In summary, IL-17 can be produced by innate and adaptive cells, but more profoundly from innate
sentinel cells of the immune system. The nTh17 is a novel subset that is thymic-\hspace{0pt}dependent
and shows a distinct developmental pathway from iTh17 cells that are derived from naive T cells.

In summary, IL-17 can be produced by innate and adaptive cells, but more profoundly from innate
sentinel cells of the immune system. The nTh17 is a novel subset that is thymic"-dependent and shows a
distinct developmental pathway from iTh17 cells that are derived from naive T cells.

\end{document}

Of course you can also get

                     thymic-dep-
endent

which is horrible. If you aren't afraid of hideous hyphenation of composite words, the shorthand is for you. If you're careful about your typesetting, you'll take your time in analyzing what hyphens in compound words are really necessary. And maybe try changing the wording, instead of allowing a hyphen.