Kanna is a certain type of magician called an onmyouji. Although this word is sometimes translated as "diviner" or "exorcist," these are incomplete definitions, since each of these things are only part what comprises onmyoudou - the skills that onmyouji practice. Since there is no simple, direct translation that fully covers all of the particular skills of an onmyouji does, we're using the transliteration of the word.
Kanna and her Sengoku allies and enemies are able to communicate with the denizens of their new home through the magic of Maple World. Thus, their text dialogue will be translated.
Since she is from ancient Japan and her primary language is Japanese, Kanna voice is in Japanese. Her animated video has subtitles, and she speaks when performing some skills. The male version of Kanna has also been given voiceovers when performing certain skills.