Just to be sure I understand...if I want to make "eil" plural, I would follow the rules for single vowels, since "ei" isn't considered a diphthong, right? (Which would make the plural form, well, "eil.")
Oh, also, I noticed the chart in Lesson 9 says ai remains ai across the board, but in the examples, taith becomes teith, and so on, so I think there's a typo....
Yeah I still haven't finished editing the lesson but other things I've done were published, so that one got published half incomplete. These are some of the changes: AI -> AI not EI. EI is a diphthong, and yes the plural of Eil is probably Eil, but could be Îl.
I should get a chance to do finish this next week for you all, apologies for the confusion.