It's strange that Libre Office don't have Spanish included on the available languages. It's because the Libre Office don't support Spanish yet, or this portable version is compiled without Spanish? (I prefer Catalan but its less common!).
"LibreOffice Portable is a multilingual package that includes support for Czech, Chinese (Simplifed and Traditional), Danish, Dutch, English, French, German, Greek, Hebrew, Hungarian, Korean, Italian, Japanese, Polish, Portuguese and Russian."