Since the ePub3 specs neither prohibit nor require
localStorage support I created a very simple test epub and the 4 apps that I tested it with (
ADE 4.0.3 Azardi 38,
Gitden Reader 4.4.9d and
iBooks 3.2) all supported it.
However, I'm wondering whether dedicated ebook readers with ePub 3 support generally support localStorage or whether this is an unintentional app-only feature provided by the rendering engine.
I'm also interested in finding out whether epub3-enabled ebook readers finally support RTL languages such as Hebrew and Arabic.
If you have an ebook reader (or an app other than ADE, Azardi, Gitden or iBooks) that supports epub3 according to the manufacturer, please download the test file, select the first chapter and tap the Off button. This should hide the blue English translations above the German text. Then close the book and reopen it. If the blue text is still hidden, your reader supports localStorage. Then select the last chapter and compare it with the screenshot.