Brother this is a new update and translator have lots of games to translate. They are not occupied with one game, if you check dazed's history he has been uploading lots of other games too, have some patience or learn Japanese yourself!
You can only do it with basic attacks afaik, so you need high Strength and enough Agility for multiple attacks. 9999 is the damage cap for a single attack, and basic attacks are the only way to get off more than one attack in a single action.
I don't quite recall the first quest you mentioned, but as for the Forgotten Island, if you can't find the NPC, sleep at the inn on the island. That map cycles between day and night, changing who you encounter.
Oh, that ones on the Nameless Island as well, in the dungeon. Search the lower floors, which are the Monastery Underground and the Heretic Temple.
98% is the limit for the base game. The later expansion lets you 100%, but it's not translated yet afaik
