Do a series has to be entered in her original language or do we create one series per language?
This series https://www.comicogs.com/series/18819-alexander-nikopol is originaly a french series, my opinion is that to keep the original language is a better option.
You are right: The name of the series should be in the original language. For example, this thread discusses that:
I recently added some Portuguese translations to that series, which had previously only German translations. I didn't change the series name because I was unsure of the original name.
(On my translations only the 3rd one mentions that it is the final book in the "Trilogia Nikopol". The others don't mention a series.)
Anyway, my opinion is to change it to "Nikopol", since it seems to be the way it is usually known in French.
Just a note to inform that I've changed the series title to La Trilogie Nikopol, supported by Wikipedia.