Review and improve usage of target="_blank"
Noticed a few places where we're using target="_blank" and the message to inform users the link is going to open a new browser tab/window is missing or hardcoded:
1 Onboarding WIzard failure message: to make this message appear, just set "Offline" in the Chrome console network panel and click on the "Next" button:

in this case, the message is missing.
2 Dashboard widget:

- on the first 2 links, there's a hardcoded string
( Opens in a new browser tab )which is not translatable - on the link in the footer, the message is missing
Worth noting WordPress has started using icons to give also a visual indication of links with target="_blank". See for example the "nearby events" widget. This is not a standard yet across WordPress, but maybe worth considering to use it.

There's now also the Cornerstone checkbox, its label has a link with target="_blank". See #439 and https://github.com/Yoast/wordpress-seo/issues/7288