NIS America essentially does touch ups to make things better and English localization both the English dub and the English text for a Japanese voiced version of a game. They've done a lot of good work over the years and brought forth a lot of good franchises: Disgaea, Hyperdimension Neptunia, the Artelier series of games, all the Ar series games, the Ys series, and much more. Many of these games have caught on with a western audience and for the most part brought more success to the NIS company therefore establishing the NIS America branch as a success and worth the time to keep.
This button is a link to Wikipedia which shows the MASSIVE amount of games released by NIS and NIS America:
The quality of the games, the voice work, and the English translation became so awkward that the job of localizing the Neptunia series of games was taken away from NIS directly and given to Idea Factory/Compile Hearts (who developed games for NIS). The Witch and the Hundred Knights was so full of glitches and bugs that it would crash near the end game on PS3 and the PS4 refresh wasn't much better. ArNosurge: Ode To An Unborn Star was a mess. These games could all have used a massive overhaul and clean-up as well as much better dialogue fixes but nothing NIS has worked on or been a part of over the past couple years but nothing has been as bad as this game:
The translation and localization was utter garbage. Pure and utter garbage. It was so bad that NIS America had to issue a public apology to the fans that bought the game saying it was awful and that they planned to patch it. And patch it they had to, the game was awful. It was later revealed that NIS America was so lazy in their localization that they actually used Google Translate to change the Japanese words to English and thus the English voice acting followed suit. GOOGLE TRANSLATE. GOOGLE TRANSLATE. That is atrocious; no one should use Google Translate to change Japanese to English because it doesn't properly translate but you especially shouldn't use it if you are a professional company who's job it is to do touch ups and translation.
Words couldn't describe how mad I was not because of the Google Translate but because of me seeing NIS America's apology notice just before I planned to start the game and that I means I couldn't play it. That means that even though I planned to play the game in Japanese that I know the English text wouldn't be done well or make any sense. NIS America said they had to re-record all of the dialogue in English, re-translate everything properly, and do several other touch ups to make the game playable and proper.
Below is a video, in English, showing the difference pre and post patch with the voices and text and some of the original, while passable, you can tell makes really no sense in English but the post patch was properly translated and put together well.
That being said, with them handing off direct localization jobs to the games actual developers like Compile Hearts for the Neptunia series has led to better things for that series. Compile Hearts even went so far as to re-do all of their Neptunia games that NIS did localization for and do them again with their own team working on it. The Re-Birth series was released for the Vita and PC, which unfortunately was bad for the PS3 owners but given these versions came out long after their own so they weren't given the same patches that a game like Ys VIII was given.