This library has the potential to have localization built-in. Currently, all strings are hardcoded in this library, especially in the derive part, but with localized strings, they have to live in some data structure providing strings per language.

The "obvious" crate for localization is fluent.

To tackle the design there are several issues that we need to address:

• Localized description from the markdown file.
• Localized help string for arguments.
• Localized error messages.

Markdown file

Recall that a command is documented in a markdown file, which is referenced like this:

#[derive(Arguments)]
#[arguments(file = "some/path/to/the/help/file.md")]
enum Arg { ... }

That works great for a single file, but we might need some more flexibility.

Instead, we need some regex-like / glob-like pattern:

#[derive(Arguments)]
#[arguments(file = "some/path/to/the/help/file-{LOCALE}.md")]
enum Arg { ... }

or

#[derive(Arguments)]
#[arguments(file = "some/{LOCALE}/path/to/the/help/file.md")]
enum Arg { ... }

Every file with that pattern would be included in the binary and the right text would be selected at runtime.

Options

The help text for the options could be written in fluent files. Ideally, this would be parsed at compile-time, somehow.

Errors

Errors would also need to be written in fluent. This goes for all errors in the coreutils, but also for the errors produced by this library.