i thought Hyde was pronounced "hai-do" as i've read on a website. and i have no clue how to pronounce hide, i've always calle him just "hide".
anyways, from what i've read and learned from french class, L'arc~en~Ciel means "the arc in sky" and it means rainbow (and it's also translated "rainbow" in chinese). Dir en Grey means Coin-in-grey. "Dir" is German for coin, "en" means "in" from french, and "grey" is just english.