Review user facing wording (meta issue)

Describe the bug Reported by Gaja, @danimo, @SamuelWei and others:

there's [...] a wild mixture of "has ended", "was ended", "has terminated" and "was terminated"

let's review and make more uniform these.

there are translation-strings for language-names, I am not at all sure if that is a good idea – I think every language-name should be written in its own language just like Wikipedia does (e.g. Deutsch – English – Norsk – Русский – ελληνικά)

Let's review why we did that.

plural forms should be handled by translation framework, and shouldn't just be two strings for singular and plural. Reason: some languages have special cases for numbers other than 1 and many. 0 comes to mind.

• Some sentences end with period . but not all. Difficult to tell within Transifex if the string will be concatenated into a bigger string.

• "app.learningDashboard.learnMoreLinkText": "this article", -- quite ambiguous.

BBB version: BigBlueButton ~3.0.0-rc.2