Polyglossia with Russian language set does not render -- and --- and nice quotes

Question

Using polyglossia package with \setdefaultlanguage{russian} stops producing en-dashes and em-dashes from -- and ---, respectively. Also, no more nice 'upper 99' quotemarks (or any other nice quotemarks) from U+0022.

With \setdefaultlanguage{english} or with default language I get those. With russian I don't. The closest I've come was with babelshorthands=true option, but there are three issues:

1. the rendering result doesn't look nice (line thickness visibly varies, at least with this font),
2. spacing with "-- (or "--~ for that matter) and linebreak after "---,
3. and of course having to use sequences which are mightily inconvenient if writing text in Russian.

I could of course directly input U+2014 and U+2015 and nice quotemarks, but why the package exhibits such strange behaviour at all? No language set (English?) works nice.

I need hyphenation, or I'd just ditch polyglossia, and babel conflicts with something I need.

The MWE:

\documentclass{article}
\usepackage{fontspec}
\setmainfont{Liberation Serif}[Ligatures=TeX]
\newfontfamily\cyrillicfont{Liberation Serif}[Script=Cyrillic]
\usepackage{polyglossia}
% these work (german - in its own specific manner):
%\setdefaultlanguage{english}
%\setdefaultlanguage[babelshorthands=true]{german}
% these don't (strange results with babelshorthands on):
\setdefaultlanguage[babelshorthands=true]{russian}
%\setdefaultlanguage[babelshorthands=false]{russian}
%\setdefaultlanguage{russian}
% polyglossia version: 2023/02/11 v1.60
\begin{document}
..........
-- ~ "en-dash"
--- ~ "em-dash"
"-- ~ "babelshorthands en-dash"
"--- ~ "babelshorthands em-dash"
\end{document}

UPDATE: The suggested reference 'Quotes don't work with polyglossia?', while it offers a solution actually, doesn't qualify as a 'precise' duplicate, I think, because the OP's question there is formulated in such way so that's easy to miss the issue's relation to my question.

Answer 1

With \newfontfamily you need to enable TeX-Ligatures, if they should be uses, e.g., for -- or --- or also for quotes. Use

\newfontfamily\cyrillicfont{Liberation Serif}[Script=Cyrillic,Ligatures=TeX]

similar to your already used:

\setmainfont{Liberation Serif}[Ligatures=TeX]

(BTW: Usually Ligatures=TeX is already set for the main font and therefore not needed.) See also question “Quotes don't work with polyglossia?”

Additionally I would suggest to use package csquotes for the quotation as shown in this answer. Depending on the quotation style you want, you can additionally use option style, e.g.

\usepackage[style=american]{csquotes}

However it seems, that the babel shorthands "--~ and "--- do not work correctly with polyglossia:

\documentclass{article}
\usepackage{fontspec}
\setmainfont{Liberation Serif}
%\usepackage[english,main=russian]{babel}
\setmainfont{Liberation Serif}[Ligatures=TeX]
\newfontfamily\cyrillicfont{Liberation Serif}[Script=Cyrillic]
\usepackage{polyglossia}
\setdefaultlanguage[babelshorthands=true]{russian}
\setotherlanguage{english}
\usepackage[style=american]{csquotes}
\defineshorthand{"`}{\openautoquote}
\defineshorthand{"'}{\closeautoquote}
\begin{document}
\selectlanguage{english}\useshorthands{"}
-- ``en-dash''
--- ``em-dash''
"--~ ``babelshorthands em-dash no space''
"--- ``babelshorthands em-dash small space''
\selectlanguage{russian}
-- "`тире"'
--- "`рывок"'
"--~ "`вавилонские сокращения, тире, нет места"'
"--- "`вавилонская стенография em-dash маленькое пространство"'
\end{document}

You would need to redefine these shorthands, too, but IMHO it is easier to use babel instead of polyglossia if you want to use babel shorthands:

\documentclass{article}
\usepackage{fontspec}
\setmainfont{Liberation Serif}% explicit option [Ligatures=TeX] not needed
\usepackage[english,main=russian]{babel}
\usepackage[style=american]{csquotes}
\defineshorthand{"`}{\openautoquote}
\defineshorthand{"'}{\closeautoquote}
\begin{document}
\selectlanguage{english}
-- ``en-dash''
--- ``em-dash''
"--~ ``babelshorthands em-dash no space''
"--- ``babelshorthands em-dash small space''
\selectlanguage{russian}
% Note: All translations by translate.google.com
-- "`тире"'
--- "`рывок"'
"--~ "`вавилонские сокращения, тире, нет места"'
"--- "`вавилонская стенография em-dash маленькое пространство"'
\end{document}

Because babel shorthands are language depending, "--~ and "--- are ignored in the English part.