I don’t think I tried to add a new item since I added “L” in my ArticleStrings setting. I thought a “Scan Library” would be enough to take the change into account (actually I’m pretty sure it did for my other newly added articles like “Le” or “La” but I might be mistaken).
Anyway I just tried the Plex Dance but it didn’t a change a thing. FYI, I’m using a docker container on a Synology NAS with the very last DSM version and here is my ArticleStrings setting:
ArticleStrings="a, an, the, un, une, des, l, la, le, les"
About your last point (the “Another thought”): I thought the same thing, that’s why I wrote this in my first message:
If the devs confirm this, then the only way would be an enhancement in Plex in order to support this 
