Re: Fallback fonts in LaTeX export for non latin scripts

[Ihor Radchenko <yantar92@posteo.net>]

Juan Manuel Macías <maciaschain@posteo.net> writes:

>> The idea is to allow
>>
>> #+language: Austrian German, Greek
>> as a valid specifier, in addition to
>>
>> #+language: de-at, el
>>
>> Then, across Org, we will make use of the standardized language
>> abbreviations.
>
> In LaTeX, as I mentioned, things are complicated. There is Babel and
> Polyglossia, and there is LuaTeX and XeTeX. In addition, there is also
> pdfTeX, which is still the default engine and (to be honest) is the
> engine used by a high percentage of LaTeX users. Although perhaps things
> will change soon to the detriment of LuaTeX. Both babel and polyglossia
> could be supported, but that means more work, more code, and more
> complications. And we are not sure that polyglossia is no longer
> maintained. After all, babel is the official LaTeX package for language
> support, and polyglossia appeared at a time when babel had no support
> for the new unicode engines. Now Babel supports all of that and is much
> more powerful, but its interface has also grown in complexity. There is
> the problem of the double syntax for loading languages: the old one,
> which loads traditional ldf files, and the modern one (\babelprovide),
> which loads languages using ini files. It is more powerful, with more
> options, but has added more verbosity to babel. I have taken advantage
> of \babelprovide, specifically its onchar=id fonts property, to
> automatically apply fonts to non-Latin scripts.

> ...
> multilingual support that does not exist as such. It is more like font
> support for non-Latin languages. And only in LaTeX, and specifically in
> LuaLaTeX. Furthermore, the user could mix languages that in Babel are
> loaded through ldf and others through ini files. For example, something
> like this:
>
> #+language: spanish, english, french, russian
>
> in Babel it would be:
>
> \usepackage[english,french,spanish]{babel}
>
> and here we need babelprovide for the font (and load Russian via ini
> file):
>
> \babelprovide[onchar=id fonts, import]{russian}
> \babelfont[russian]{rm}[options]{somefont}
>
> Org would have to discern which name refers to a non-Latin language
> (which wouldn't be complicated with the functionality you're working on)
> and then apply the default font by adding a line with \babelprovide.
>
> Of course, English, French and Spanish can also be loaded via ini files:
>
> \babelprovide[main,import]{spanish}
> \babelprovide[import]{french}
> \babelprovide[import]{english}
>
> Even babel also supports:
>
> \usepackage[english,french,spanish,provide*=*]{babel}
>
> but in that line we cannot put Russian with onchar, etc. And then there
> is pdfTeX, where only the classic babel syntax is allowed, without any
> "*provide".

Aren't we already handling this problem in `org-latex-make-preamble'?

>> My idea was that
>>
>> #+language: ancientgreek russian arabic
>>
>> implies "use default font for arabic", unless #+latex_font is specified.
>
> This seems the most consistent to me for Org, but, as I mentioned in the
> other email, I have some concerns. Currently, what we are talking about
> is simply font support for non-Latin languages. If it is allowed, in the
> current state of things, that #+language can accept a list of language
> names, we can give the user a wrong perception of reality. That is:

 <complications with full support not being possible in all the LaTeX flavors>

> In short, I find everything very confusing. I am not opposed to doing it
> as you propose (in fact, it is the option I like the most, especially
> when org is polyglot in the future), but I also want to warn of possible
> complications.
>
> Therefore, since we are, for now, with fonts for non-Latin languages, I
> think it should be made clear that the keyword is about fonts (and about
> LuaLaTeX). Maybe through two keywords:
>
> #+lualatex_fonts_for: language(s)
> #+lualatex_fonts[language(s)]: "font" options
>
> ?
>
> I think it's ugly, but I can't think of anything else.

Maybe just

#+lualatex_fonts[languages(s)]: default

to force the default.

> By the way, and as a side note, is it currently possible in Org to
> define a keyword within :options-alist of the style #+foo[anything] or
> would something like org-collect-keywords have to be modified?

We will need to add things to `org-element-dual-keywords' and make sure
that the code expects the keyword value to be a list, as returned by the
parser. AFAIU, it should be enough.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>