http://archives.bulbagarden.net/media/upload/2/22/AG145_noodles.png
The reference to China during the Kanto Battle Frontier.
Um, but the accent is clearly put-on. The voice actress is Japanese, she's just playing the role of a character who does not speak Japanese well because Melissa is not Japanese.
The Japanese version of Pokemon generally uses highly prolific seiyuu who are VERY talented and serious about their jobs.
The accent, English name, and her use of English words are purposefully used to show she's a foreigner, not to mention her great height (just as they did with Mattise), because Asians are generally shorter than Europeans. xD;
It's part of the script and her character, not a problem with the seiyuu.
Your argument makes no sense. So what if Pokemon is fictional? Different lands do exist in it, whether you'd like to believe that or not.
Really, why shouldn't there be? Many fictional worlds are made up of many different countries and many works of fiction take place in alternate versions of our own world. Pokemon does not cease to be fiction by bringing in (their version of) real world countries.
How about characters like Fuu and Lan (Tate and Liza), with Chinese names and outfits inspired by traditional Chinese dress?
Pokemon characters are often Japanese, but some are Chinese, American, Italian (see movie five), Greek (Damos, Sheena, Kevin, and just about every one in the Arceus movie), and possibly other nationalities as well!
Don't forget Hollywood existing in early Kanto!
Or the various wars mentioned and even seen briefly over the course of the series (although taking place in the past of the Pokemon World).