Remove locale from react-i18n now that it is available in i18n-utils

[p-jackson]

Changes proposed in this Pull Request

The react-i18n library currently supplies the current locale slug, however that package is trying to do things in a way that will work for any Gutenberg user, and there is no standard way to access the current locale slug in Gutenberg/core WP.

Since #47566 the @automattic/i18n-utils package has had the ability to supply a locale slug, and after #47567 is merged there will no longer be any references to the locale from react-i18n. So this PR removes it.

• Remove i18nLocale from the useI18n() hook
• Update readme

Testing instructions

• There should be no references to i18nLocale after Update Gutenboarding to use new <LocaleProvider> #47567 has merged, so nothing specific to test other than smoke testing

[matticbot]

Test live: https://calypso.live/?branch=try/locale-context-in-i18n-utils

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~103 bytes removed 📉 [gzipped])

name                 parsed_size           gzip_size
entry-main                -111 B  (-0.0%)      -54 B  (-0.0%)
entry-gutenboarding       -111 B  (-0.0%)      -49 B  (-0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[lsl]

Approach lgtm.

i18n-utils isn't yet safe to import unless you're ok with bringing in i18n-calypso along with it. (We're trying to avoid this - why its so difficult to untangle)

^that coupling will be fixed up with #47358 which replaces i18n-calypso's getLocaleSlug with react-i18n's i18nLocale value instead.

Of course #47358 depends on your work in #47352 which is what makes the locale available in react-i18n.

Bit of a chicken and egg situation as this PR then removes that locale from react-i18n. I guess we need to use this new provider and set the locale along side setting the localeData in react-i18n in components/calypso-i18n-provider

There is a getLocaleSlug in the i18n-calypso that should be usable for this.

phew - round abouts but I think this will work.

[lsl]

Followed up on this here #47492

[matticbot]

Caution: This PR affects files in the Editing Toolkit Plugin on WordPress.com
Please ensure your changes work on WordPress.com before merging.

D52928-code has been created so you can easily test it on your sandbox. See this FieldGuide page about developing the Editing Toolkit Plugin for more info: PCYsg-ly5-p2

Big changes since this review. This PR no longer tries to do everything and just removes i18nLocale from the the react-i18n package one all references to it have been removed.

[p-jackson]

Done by #47352