i18n: a locale per app, catalogs of messages, mirrored stacks

i18n::I18n is a gpui global holding the shown locale and one catalog of
messages per locale. text fills each {name} from its arguments; a
missing key, argument or catalog fails, and every catalog holds the
first one's keys. Locale writes numbers with its separators and dates
in CLDR's short numeric form; Hebrew replaces Arabic, whose Egyptian
digits Ely does not write. Direction::row mirrors a stack and
Direction::align sets text against the reading side. The gallery's
chapter 40 shows the messages in seven locales, every locale's number
and date, and a file list that mirrors under Hebrew.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib.rs

@@ -20,6 +20,7 @@ pub mod finance;
 pub mod forms;
 pub mod generative;
 pub mod git;
+pub mod i18n;
 pub mod interaction;
 pub mod layout;
 pub mod lists;