Alias Encoding allows your UTAU to understand two languages at once. First, open up UTAU, and make sure you have all of the samples you need. Then click (T) then (S). It should open up all of your samples. Find a sample you want to alias. For example find 'a', click it, then second box from the top, paste 'あ'. Now click OK. Now when UTAU runs hiragana UST's, 'a' will be scanned as hiragana and romaji.