As you have already explained in the text that it is a saying, I would just italicise it and put a dash in front, I think that would look nice and be easy to read, like this: Life has a way of taking unexpected turns, or as a German saying goes ~Der Mensch denkt, Gott lenkt - God proposes, man disposes.
I would include the meaning in English as well - otherwise it's meaningless to non German speaking readers.
The second one - I would keep the quotes - it makes the moment more dramatic and interesting, like it's happening now, and we, the readers are standing there in the shop, as viewers - I actually saw the whole scene in my imagination, as if I was there - and that's a good thing!
I would not italicise it, just leave as is.
It might help to have some kind of break between the quote and 'I was devastated'. A dash, or put 'I was devastated' all on its own on the next line. It's a dramatic moment - so give the reader a moment to feel - that devastation. By putting space around it.
However, when I told them I was pregnant, I was out the door! "We cannot have a pregnant woman stand behind the counter and serve our clients. How would that look?"
...I was devastated.
I added an exclamation mark, to heighten the expression of surprise. And a few dots to show that - she gasped, inwardly. An internal... pause.
If it's just reported speech it's always much drier. For example 'the accused drove away in a cortina' is much more boring than 'open the door, John, we have to get away now!'
It is also more engaging, interesting, and real, to readers when their minds must do something to imagine the situation - so, make them do some work - it's good for them! - rather than the data being served to them on a tin tri-partate plate!
I found this useful link in a related question. It talks about how the usage of quotation marks has changed in this century and explains how different mores currently apply for italicisation in novels and newspapers. Coming from the background of typesetting really.