Since the anime came out in 2009, Juvia has been given a voice to match her character. That voice is Nakahara Mai. Here is a brief profile on her:
Name: Nakahara Mai (中原 麻衣)
Birth Name: Abe Maiko (阿部 麻衣子)
Birthdate: February 23, 1981
Birthplace: Kitakyushu, Fukuoka, Japan
Blood Type: AB
Profession: Seiyuu (2002–present), singer (2004-present)
Hobbies: Kendo, cooking, watching movies
Nakahara Mai seems to have one of those initially soft voices. She is good at portraying shy, innocent or quiet characters. This was my initial thought of Nakahara. The first time i really took notice of her was as Juvia. However as I looked into her more, the more i found her voice behind other beloved characters: Karin from Kamichama Karin, Nagisa from CLANNAD, Nora from Spice & Wolf and lastly Zakuro from Otome Youkai Zakuro. Most of my Nakahara experience has been quiet, shy or innocent girls. The exception being Zakuro and sometimes Juvia.
Nakahara does bring these qualities to Juvia though. But it's more then that. When Juvia is first introduced to Gray she says calmly and seriously "falling so gently...yes, Juvia is a rain woman, one of Element 4.". Just moments later though she blushes, looks away and says rather shyly and nervously "I see. Juvia has lost. Have a nice day!". I like that Nakahara is able to capture those quick changes in Juvia's feelings and temperament. I think what has impressed me the most about her performance thus far is when Juvia finally snaps again Meredy. I don't think I've ever heard her voice quite like that before...or since.
Since 2011, Funimation has been bringing the Fairy Tail series over to western audiences. Brina was picked to be the actress for Juvia. Here is a brief profile on her:
Name: Brina Michelle Palencia
Birthdate: February 13, 1984
Birthplace: Owasso, Oklahoma
Family: Gino Palencia
Profession: Voice Actress, Actress, Singer, ADR Director
Education: BA in Music from University of North Texas
Agency: Mary Collins Agency
I admit i don't know much about her other than what I've seen on GameStop TVs. Which im trying to not let taint my opinion. ^^; I'm not familiar with her voice work or the dubbing work in general for Fairy Tail. I try not to be biased but just in general I prefer to watch shows, etc. in their native language. Whether that language is Spanish, French or Japanese.
She is apparently well known for adult female voices. I'm not sure if they just mean a generalized adult woman or just a mature sounding voice. I could see Juvia needing that type of voice initially as she comes off as a rather serious and calm person. However she can also spontaneously be bubbly, excited, happy, shy, nervous, etc. I did notice she voiced Kurono Kurumu from Rosario + Vampire, who might be seen as similar to Juvia at times. I will try to add my thoughts and opinions upon watching a dubbed episode