utf-8-safe replacement for strtr()?

i havea general replacement or workaround for every php function in my code that i know to be utf-8-unsafe. except one: strtr(). the only ideas i have to implement strtr in php with known utf-8-safe php functions would be rather inefficient. any ideas, suggestions, pointers? or maybe you're better at googling an answer than i am. assume mbstring is available. tia tom