you can learn hiragana und katakana within 6 hours. just try the book "remembering the kana".
that helps a lot in JRPG´s to read item names, location names and so on. after that you can start to learn the 2000+ kanji and after that: vocabulary.
its the way i try to learn japanese, already learned the kana and 100 kanji right now (1 year learning time).
dragon slayer II is beatable with a good guide at hand, there is one for the SFC version on gamefaqs. perfectly usable for the PCE version. but DS II is not the greatest game to start getting into JRPG´s. there are much better choices like neo metal fantasy, tengai makyou games, tenshi no uta games...