Translation credits: Include more information

Also fixes a typo that went unnoticed for long - sorry about that!
Translation credits: Large update (#1996)

Okay, so first of all there's no excuse for how lazy and unorganized we
were in the past when it came to giving due credit for our translations.
None whatsoever. We just screwed it up badly and always found a nice
excuse for putting off the work. This above everyone else holds true for
me personally. For some of these fine folks it has been more than two
years now until we're finally remembering who did hard work for us.
To everyone who was affected, or still is: Please accept my apologies.

There are many dark hallways in which data got stuck and lost. In case
you find yourself still missing in our translation credits: Please do
contact us with the details you remember. We will figure out the rest.

We'll approach some registered users of our various pootle servers where
no or no feasible contribution data survived. In the past we had some
kind of informal guideline that required 10-ish submitted strings in
pootle for users to be included in the credits. Those users will most
likely also be mailed by us to potentially be included.

So, hat in hand, sorry again about all this mess. At least the future is
brighter, they say - proper credit is given by our new platform Weblate,
even for user suggestions, and right in the Author field of commits.