I don't know who came up with the romanisation of "oslatte", but I'm gonna offer a slightly different alternative. Since it's a portmanteau of オスラ ("osura") and オスって ("osutte"), which in turn are derived from the Japanese spellings of Au Ra and Miqo'te combined with オス ("osu"="male"), it makes much more sense to me to call the pairing "osura'te" in English.