First implementation to display multilingual email parts (RFC8255)

[igit]

Written during the #IETFHackathon [1] of the #IETF101 [2].
[1] : https://trac.ietf.org/trac/ietf/meeting/wiki/101hackathon
[2] : https://www.ietf.org/how/meetings/101/

This code is not stable nor correct regarding to the neomutt code style / contribution guide.
This just demonstrated the Proof Of Concept to display in a MUA email build with RFC8255.

[flatcap]

Thanks for the code @igit -- very interesting.

This code is not stable nor correct regarding to the neomutt code style / contribution guide.

hehe, not a problem. clang-format will sort out most of that for us.

It would be really helpful if you could attach a sample email for us to test.
Perhaps, "hello world" in three languages.

[jindraj]

@flatcap Maybe examples from RFC8255 could be sufficient for testing https://trac.tools.ietf.org/html/rfc8255#section-8 + @igit has a repo https://github.com/igit/rfc8255-reflector which could be quite useful for testing too.

[igit]

@flatcap @jindraj Thank you guys for regarding this code !
You can play with the online reflector at this recipient address :
reflector[... config ...]@rfc8255.as-home.fr
See the "How to use" in https://github.com/igit/rfc8255-reflector/blob/master/README.md to set the good plus-addressing config (ex: reflector+sl_en+tl_fr+tl_es+tl_de@rfc8255.as-home.fr).

Please let's me know if it (the reflector) works fine for you.

[bortzmeyer]

Congratulations, this is great work. What about one or two screenshots for the poeple who hesitate to try the patch?

[igit]

Here is a UI example with an english message sent to the reflector to be translated to "fr", "es", "zh" and "ar" and replied with RFC8255 email.

[flatcap]

I've given it a try and it works (you knew that :-)
I've also played with your reflector -- very fun.

I've run the code through clang-format and given it a tidy -- see the commit message for the details.
I've also added the RFC text with the 3 examples cut out -- just for testing purposes (we can drop the commit before merging).

Your code looks reasonable. I still have more testing to do.

Your code reads the multi-lingual parts.
It would be nice if we can extend #734 so that we can create them too.

[walkerlala]

How do you get those emoji displayed in the pager?

[walkerlala]

This series of patches look good to me. I will add support for writing multipart/multilingual emails in branch https://github.com/neomutt/neomutt/tree/devel/multipartalternative

[walkerlala]

@flatcap @igit Can I apply the patch to branch [devel/multipartalternative] so that I can directly develop on that branch?. All the commit messages will be leave intact (it seems like a rebase). Also, there is a bug in viewing the multilingual message: when there is no Content-Language header in every part of a multilingual email, neomutt will show nothing. It will be easier for me to fix that if all the commits are rebased to [devel/multipartalternative].

[walkerlala]

@igit I have just transfer you commits to branch [multipart/alternative] (see #734) and fix a bug on top of it. If you have time please review that in case I miss anything.

@flatcap please review.

[flatcap]

Merged as part of #734