If Ikaruga was an imperial nation, then it may be subdivided into regional nations (kuni). However, kuni can also refer to a province or region, rather than an independently-ruled country that makes up part of a larger sovereign empire. If it had been oukoku, rather than simply kuni, then that would clarify things a bit more, implying a great deal more fractiousness in Ikaruga.

The name of Bang's story in CS "Lost ARCH ENEMY" has a double meaning. It can refer to Bang having lost Jin as his arch enemy, since Trinity told him about his true enemy(the system of the NOL). It can however also refer to the last and missing Nox Nyctores Bang possesses(Rettenjou), since Nox Nyctores are called Arch Enemies in Japan.

Uh, that's the point of double entendres, you know...? Since the meaning is ambiguous, some people may interpret words in a different way. Most of the non-Japanese people, who only play in English would probably never understand the other meaning, since Arch Enemies were localized, Bang's story name however was not. There is not just one interpretation behind the story name. Japanese people love to play with words, that's why I think this deserves a trivia remark to explain this. I would totally agree with you if Aksys had localized Bang's story title, but they haven't.

1. Since they localized the game first in the US, it might have sounded a bit awkward for natives. The point is that the weapons sound somehow foreign for the people playing. Everything else(in the jap-dub) was in Japanese or at the least is based on Japanese mythology etc., while the Nox Nyctores, as special weapons are kind of from a foreign world. Though the name itself, including the titles Detonator and Highlander are the exceptions.

2. Consistency. Ars Magus is Latin, the NOL is Latin, even the titles of the NNs are in Latin(including Ignis), so it would have sounded a bit off if the weapons had an English term/name, with the exceptions of the NNs explicit names, since... well, they are proper names(yes, I purposely repeated myself just now ;D). Although I never would have guessed what exactly the meaning of seithr or Ars is without a lexicon/dictionary. Giving them foreign sounding terms is maybe a bit too consistent, since these terms were actually in proper Japanese.

And yeah, "Lost NOX NYCTORES" might have sounded a bit funny at first, but then everyone would have immediately understood the message. I'm pretty sure this double entendre is intended and many people do not understand the hidden meaning behind this title.

Edit: One more thing. The term Sankishin is obviously kept in Japanese to emphasize the focus on the three Japanese gods Amaterasu, Susanooh and Tsukuyomi, as well as the three sacred treasures. However, then I must wonder why exactly they translated "the sword of Izanami" with "the sword of the Imperator"...