Sharing: When switching site language, switch sharing label's language automatically

[kathrynwp]

When switching a site's language, the Sharing label remains in the language the blog was originally created.

Ideally, when a user switches the site's language, the label's language should change automatically to save the user from having to figure out where to change the text.

Steps to reproduce the issue

1. Create a site with the language set to English US.
2. Go into Settings > General and select a language for which Jetpack is fully translated – such as French France (FR_fr) – and activate it.
3. Activate the Sharing module and set the sharing icons to display on posts.
4. Visit a post on the front end.

What I expected

The label above the sharing icons should be in French.

What happened instead

The label above the sharing icons was still in English.

Replicated in multiple themes in multiple languages, here are two examples:

The only way to modify the sharing label's language at this point is to manually go into Sharing Settings and adjust the text by hand there:

WP Admin

Calypso

No written user report, I noticed the issue while helping a user in person at a local WordPress event.

[stale[bot]]

This issue has been marked as stale. This happened because:

• It has been inactive in the past 6 months.
• It hasn’t been labeled `[Pri] Blocker`, `[Pri] High`.

No further action is needed. But it's worth checking if this ticket has clear reproduction steps and it is still reproducible. Feel free to close this issue if you think it's not valid anymore — if you do, please add a brief explanation.