fix(v2): restore Algolia search

[lex111]

Motivation

Fixes #3826

If i18n is not used, locale will be undefined then, so we shouldn't include it in Algolia's facet filters.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Preview.

Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/docusaurus, and link to your PR here.)

[netlify]

Deploy preview for docusaurus-2 ready!

Built with commit 360b535

https://deploy-preview-3828--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	69
🟢 Accessibility	99
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-3828--docusaurus-2.netlify.app/classic/

[lex111]

@slorber since this is a hot fix I am merging right now, but something seems to me like locale is always undefined because there is no locale in facet filters on French version site https://deploy-preview-3828--docusaurus-2.netlify.app/classic/fr/ although should be there?

[slorber]

Thanks, fixed it better here: #3829

The currentLocale is not read from the correct place, so your solution will fix the site but it would still lead to a problem.

[slorber]

ahhh tooo late :D

[github-actions]

Size Change: +19 B (0%)

Total Size: 156 kB

ℹ️ View Unchanged

Filename	Size	Change
website/build/blog/2017/12/14/introducing-docusaurus/index.html	20.7 kB	+1 B
website/build/docs/introduction/index.html	180 B	0 B
website/build/index.html	5.87 kB	0 B
website/build/main.********.js	112 kB	+18 B (0%)
website/build/styles.********.css	17.4 kB	0 B

_{compressed-size-action}

[lex111]

Oops sorry :)

[slorber]

will update my PR with a proper fix

Note: there is always a current locale (en by default).

Previously we used to hardcode this locale