rule based replacement of s with ſ (long s)

Question

Is there a way in any LaTeX (LuaLaTex, LuaHBTeX, pdfTeX …) to automatically typeset a document written with standard «s» with long s (ſ) instead where appropriate? The rules seem to be mostly language independent and can be found here.

This is basically the opposite of this question.

I am aware of the OpenType character variant method and produce long s in Latex but those do not answer this question.

MWE

\documentclass{article}

\usepackage[german,english]{babel}

\begin{document}
\section{s}
In German, the s stands (please no automatic replacement)
\begin{description}
    \item[At the end of a word]
        \foreignlanguage{german}{Das Haus, des Landes}
    \item[At the end of a syllable]
        \foreignlanguage{german}{dasselbe, Eispalast, Häuschen}
    \item[word gap s if the following word is self standing]
        \foreignlanguage{german}{Donnerstag, lostreten, deswegen}
    \item[a word gap s in case of a following suffix syllable which begins with a consonant]
        \foreignlanguage{german}{Häuslein, Wachstum, nachweisbar, Weisheit}
    \item[in loan word prefix syllables dis- and des-]
        \foreignlanguage{german}{Distribution, Desinfektion}
    \item[before d, k, m, n and w]
        \foreignlanguage{german}{Dresden, brüsk, Osman, Mesner, Oswald}
\end{description}
\section {ſ}
In German, the ſ stands (in the following example words s should be replaced by ſ   )
\begin{description}
    \item[at the beginning of a word]
        \foreignlanguage{german}{so, sieben}
    \item[at the beginning and inside of syllables]
        \foreignlanguage{german}{saufen, Wunsch, erstaunen}
    \item[at the end of a syllable except composita]
        \foreignlanguage{german}{Gasse, Wasser, Bissen, fassen}
    \item[before p, t and ch (sch trigraph)]
        \foreignlanguage{german}{Knospe, fast, löschen}
\end{description}
\section{ſſ}
The double ſſ stands (double replacement desired):
\begin{description}
    \item[if there is as short vowel before the first s and any vowel is following the second s]
        \foreignlanguage{german}{Adresse, müssen, Tasse, vergessen}
    \item[if a following e is omitted by an apostroph]
        \foreignlanguage{german}{ich lass' es sein}
    \item[in flexed forms of words that end with -as, -is, -nis and -us]
        \foreignlanguage{german}{die Ananasse, Wallisser Aprikosen, des Zeugnisses, des Busses}
\end{description}
\section{ß}
The Esszet ligature ſs ß stands:
\begin{description}
    \item[at the end of a word]
        \foreignlanguage{german}{muss, nass, Biss}
    \item[at the end of a syllable]
        \foreignlanguage{german}{hässlich, vergesslich} 
    \item[before a consonant]
        \foreignlanguage{german}{lasst, hasst, wisst, verpasst, verlässlich}
    \item[after a long vowel]
        \foreignlanguage{german}{grüssen, Strasse, fliessen}
    \item[after a diphtong]
        \foreignlanguage{german}{heissen, aussen, scheusslich}
\end{description}
joking: It's that easy!

Rules courtesy of \texttt{www.deutsch-kurrentschrift.de}
\end{document}

Answer 1

I'm working on a new feature in babel for luatex meant for changes like this, although it's based on the language, so it has its limitations (after all, babel is about languages). It's based on lua patterns and here is an example:

\documentclass{article}

\usepackage[german]{babel}

\babelfont{rm}{FreeSerif}

\babelprehyphenation{german}{s[a-eg-z]}
  { string = ſ,
    {}
  }
  
\begin{document}

abcs abcsde abcsfe

\end{document}

It prints “abcs abcſde abcsfe”.

Edit. To be honest, I've found some rules a bit vague, and on other hand, some rules are clearly impossible to carry out in a more or less simple way (how to know if a word is a loan word?). So, the solution is partial, but I hope it can help for similar cases, and also as a starting point which can be used to make tests and feature requests (after all, and as I said, I'm working on it, so it's a good time!). Well, and even contribute 🙂. Some rules are defined with \babelprehyphenation and some others with \babelposthyphenation. (I think there also rules related to hyphenation, and with \babelposthyphenation the discretionaries can be modified.)

ſ before p or t

\babelprehyphenation{german}{s[pt]}
{ string = ſ,
  {}
}

Before ch

\babelprehyphenation{german}{sch}
{ string = ſ,
  {},
  {}
}

At the beginning of words

Here a special rule is necessary, which marks explicitly the text to be caught with empty matches. They are added automatically in other patterns.

\babelposthyphenation{german}{^()s()}
{ 
  string = ſ
}

Beginning of a syllable

Assuming a discretionary marks a syllable boundary. Special cases would require additional rules.

\babelposthyphenation{german}{|s}
{ 
  {},
  string = ſ
}