I’ve run into a bit of an issue with a script font I’m developing. The font has contextual alternatives for a few of the letters, so the tails fit together better, as well as don’t extend at the end of the word. I’ve been developing these by duplicating the letters, making the changes, and changing the names to letter.alt, and using the calt sub feature to sub them in. What I’m wondering is if there’s an easier way to do this with accented characters than copying and adjusting all of the characters, despite them having the same base letters.
Better extensions for what you are intending: .fina, .init, .isol, or .medi.
One example: If you have a, a.fina and dieresis, and you build adieresis.fina, then Glyphs will prefer a.fina over a for the composite glyph.
Positional features are not active by default in Adobe apps though. To answer the original question, you do need to make accented alternates as well. I think you only need to adjust the alternate base letter (just place anchors).
You can build a calt feature with .fina, .init, .isol, or .medi letters as well. A tutorial article about this is in the works.