I'm currently watching the FMA live action movie, which has Reole on its maps/subtitles. It seems as though this might also be true in the manga, at least according to this Wikia. However, Liore or Lior is the standard transliteration that I've seen for it, and I'm pretty sure that's what was used in the anime.
Both are technically (more or less) correct transliterations of リオール, but also somewhat unusual, given rs and ls are the same, and so it would usually either be Rior(u) or Liol(u). Reading from English, they also (at least to me) imply somewhat different stressing of syllables, Ree-ohl vs Lee-or.
Is there an official Hiromu Arakawa-approved way of writing it in English?