Describe the bug
When publishing an article to a site whose language is different to the current WordPress UI language, and inserting a link that opens in a new tab, the additional screen reader text " (opens in a new tab)" is appended to the aria-label in the language WordPress is set to, not the language of the specific site the article is being published at. So if my WP user interface is German, but the particular site is in English, the text gets added in German, but should be in English.

To reproduce
Steps to reproduce the behavior:

1. I am on wordpress.com, which is set to German (my native tongue). I have a site there whose language is in English.
2. Start a new post.
3. In a paragraph block, insert a link, expand the Link Options and check the Opens In A New Tab checkbox.
4. Check the resulting HTML for the link.

Expected behavior
The aria-label that contains both the link text and the addition of " (opens in a new tab)" should have that extra text in English, which is the site's language. But it actually is in German, which is the language WP is currently running in.

Screenshots
I'm blind, screenshots are difficult.

Desktop (please complete the following information):

• OS: Windows 10.
• Browser Firefox.
• Version 70.0.1

Additional context
Screen readers usually read the text of a page in a given language, in this case, English. Hearing the German equivalent of " (opens in a new tab)", " (öffnet in neuem Tab)", is unexpected and meaningless to someone not speaking German. It should be in the language the actual article text is in, which is usually determined by the setting for the Site Language under Manage/General, or Site Identity in the Customizer.