Thanks for the detailed feedback.
1. Have you tried “Popover” mode? It’s under Style in the AA tab of the reader page sidebar. Rather than inserting the translation into the line, it floats it above the text, so the layout underneath doesn’t move at all and your reading position stays put.
There’s no scroll mode at the moment, partly for technical reasons. Readlang is optimized for novel length texts and to be just as fast and responsive on those as on short ones, and putting a text like that into one huge scrollable display would slow things down a lot, at least the way it’s currently engineered.
For a sentence that gets split at a page break: while dragging to translate, if you hold over the last word on the page, everything shifts up one line to make room for an extra line, which lets you translate a phrase that runs past the end of the page.
2. I’ve made a change which should remove most of this delay. Please refresh your Readlang browser tab and let me know whether you still get the long wait after leaving the page idle for a couple of minutes.
3. This one is now implemented, as of a month ago (this reply). You can click on words and phrases within an explanation to get a translation, as long as the explanation is in your learning language.
Please let me know how you get on.