The Vagrant differs from other Origins in having particularly harsh phrases, which are often inappropriate. Life in the slums leaves a mark that is difficult to shake off. Besides, if your Vagrant has adapted better, then... just don't use those phrases. It's a matter of role-playing.
Perhaps. But why? This phrase from French is quite common in English, as far as I know. Analogous to “enjoy your meal”. In the game itself, the characters do not know any English or French, so their phrases obviously sound different. But the meaning is the same. Also, I allow myself to use words like “dude,” etc.
However, I do not allow myself to use terms that cannot exist in a Bronze Age society, even if the phenomena themselves already exist. Selene is not familiar with feminism and does not call anyone a sexist (although she encounters it constantly, one way or another). She does not mention Satan, Hell, or Heaven, and instead of God, she says gods (because there is no Christianity here). She can feel however she wants about slavery, but she cannot be for or against abolitionism simply because such a concept does not yet exist. And so on and so forth.