Add possibility to set custom messages or use different languages

[gloaguen-evan]

Hello,

I use jsonschema to validate features and I would like to be able to modify some error messages as well as to be able to offer messages in the user's language.

This is my first participation in a project and I saw that it was better to discuss in Issues before proposing a Pull Request, so here I am.

Here is my branch:
https://github.com/gloaguen-evan/jsonschema/tree/feat(messages)/add_possibility_to_set_custom_messages_and_translation

Thank you in advance for your attention regarding my request.

Evan

[Julian]

Hi there! Thanks a lot for your offer, it's very much appreciated.

There's an existing issue open at #971 -- let's move discussion there if that works.

Briefly, just scanning the branch, I think we'd want to do this using the stdlib gettext module rather than rolling our own way of indicating messages. You did quite well though, especially if indeed this is your first contribution, so yeah well done! I suspect if you try wiring gettext in you may be able to mostly delete things rather than needing to make significant changes but hard to guess.

If you do do so, I will probably have limited time to review this for at least a month or two, there are a few other things on my plate that are higher priority (for the library). Don't take that as a slight I hope!

But if you're indeed interested it'd be very much appreciated, I'd love the help. Thanks again and props for the work so far.