Yes to the general concept.
Yes to the first regional language being a freebie.
Yes to the list from GE, adding Irthian and HaGruut, but please also add Broken Common as well.
Yes to retroactive.
Yes to "ancient" versions of the languages for when the GM wants to force a linguistics check.
I guess I don't see this as any different than one GM using a lot of traps, while another uses tons of kobolds, while another uses . . . Well, you get my meaning. Any sort of challenge can be "done to death" with a little effort. If I get into an adventure that's got too much of something I don't like, I'll make sure I ask that GM before joining another if there's more of the same to be found; if there is, I'll pass on that one and catch the next.
I'd lean toward multiple languages for Landadel. Landadel seems very European to me, where there are lots of small countries / duchies / baronies / whatever, so there's something like French (for Zitteaux) and German (for Heinrich).