The following image is taken from the book Vedic Predictions of World Religions, published by Pandavana Sena/Sena Books (www.psena.com).
Hare Krishna Hare Krishna Krishna Krishna Hare
Hare Rama Hare Rama Rama Rama Hare Hare
Devanagri script is just like another kind of alphabet, so the mantra is written phonetically (according to its sound), not in any particular language, although it is considered to be Sanskrit, the mother of all languages, and original language of the vedas, including Bhagavad-Gita and Srimad-Bhagavatam.