Translation:Good evening, he is Cristian, I am George.
In addition to that, names DO change across languages. Christina/Kristina, Basil/Vasile, etc. Not your own name, but the name in and of itself changes spelling across many languages. In English, Christian is spelled with an H and this is an English translation so there's nothing wrong with either variation being used (especially when, in this example, the name is even pronounced differently between the two languages).
I disagree. While people might choose to adapt their name, the default should not be to localize everyone's name in every situation. If someone introduces themselves to you as Andrew, would you call them Andrei when speaking Romanian? I would not. From what I've seen, names in other courses on Duolingo have not been localized, and I don't think they should be here either.
Translating names is mainly a thing of the past. Johann Sebastian Bach is still called Jean-Sébastien Bach in France, though. It still happens to some degree, in special settings. I find it very interesting to learn these equivalents, and in the Latin course I have actually been missing it. I find it relevant for people to realise that the -us in Stephanus isn't a part of his name, it is just the case ending - and furthermore, the same name in English is Stephen. Now, if this course is going to translate names, it should do it with all names translatable, of course.
You're right, the two have the same origin but they evolved as different names in Romanian. Currently, both exist in Romanian and they are considered distinct names the way John and Ian are considered distinct in English despite having the same root. By contrast, Mihai (or Mihail) is a translation of Michael.