Adding translation framework based on mdbook-i18n-helpers

[dalance]

This is a proposal to add translation framework based on mdbook-i18n-helpers.
It is already supported by rustc's bootstrap process and used at Rust By Example which has Japanese and Chinese translation.
By adding the framework, each language translations can be added to this repository, and users can select a language at https://doc.rust-lang.org/edition-guide/ .

How about this idea?
If this is acceptable, I'll work to create a PR.

[traviscross]

Thanks @dalance for your interest in this work. Unfortunately, at this time, this just isn't something that we're interested in maintaining, for mostly the same reasons as described over in rust-lang/rust#133562 (comment).

[dalance]

OK. I understood.