"Cars are made in Dublin."
Translation:Déantar carranna i mBaile Átha Cliath.
If it isn't, it should be. I believe they are in the process of adding it, however.
Yes, 4) Other Words
Eclipsis is also added after the words i in, dá if, mura if/unless. https://www.duolingo.com/skill/ga/Eclipsis
but a word of caution:
Lenition occurs after the words ar on, de off, den off the, do to, don to the, faoi under/about, ó from, roimh before, sa/san in the, trí through, um around/about.
Is there any difference between "gluaisteán" and "gluaisteáin" in terms of pronouciation?
Yes; the singular ends with a broad N sound, and the plural ends with a slender N sound.