One of the common complaints regarding the localization of the original Project Diva F was that the song lyrics were in romaji, with no option for proper English subtitle translations. Well, Project Diva F 2nd is fixing that:

According to Sega's blog, they've worked directly with the original artists to ensure the accuracy of the translations. Though it also notes that translated subtitles will be available for "a majority" of its track list, so there may be some songs in the game that don't feature the option, for whatever reason.

Wow, they are really putting in work on this one. I'm impressed as hell with SEGA these last two days.

Indeed. From what I understand, the original game's localization was basically a labor of love from one member of Sega's localization staff. They really didn't put many resources behind it, and of course they were obviously unsure about it given the limited physical release and no Vita localization (at first). They were very obviously surprised with the response the game received.