HANABI is a Japanese word, but not only is the title is written in Roman letters, but it is a proper noun (the name of a place). You don't translate proper nouns, so technically "Hanabi" is both English and Japanese in this case.

The title of the song Hana is also Japanese (again, written in Roman characters instead of Japanese). Although, it is not known if Hana, too, is a proper name; rather, it seems to come from the lyrics of the song.

End roll is the re-Anglicized form of the Japanese word エンドロール endorooru. The term "end roll", as far as I know, is not an actual term used in English; we simply say "[film] credits". I suppose you could also say End roll is a Japanese title.

Humming 7/4 is partially Japanese. The Humming part is spoken as in English, but the 7/4 is spoken as Japanese: 四分七 yon bun nana, as opposed to スリークォーター suriikwootaa

kanariya is Japanese, as well. It is a Japanese word for "canary", instead of the Japanese pronunciation of the English word (which would be キャナリ kyanari)

I think she just likes the way English titles sound and look. Plus, they offer much more artistic freedom than selecting the hook line as the title (which is what record companies usually want you to do).