So after playing Napple Tale for a very brief bit, I came across this completely undecipherable sign:

It's a generic sign used throughout the game, and while you can read it in-game, that message clearly isn't the one on the board (something along the lines of "We are now in 'Spring Won't Come Vacation'"). What I could get from the sign was:

____, as well as the ef__ct delicate colour of Mucha's po__ of his experience with light__ sharp p____ with the garish the effect of light in painting ever, in the exp___ of the he w___ out his own ext____

In connection with thie___ which was?

What does this mean? What mysteries do you hold, Napple sign?

maybe it's "colour of Mucha's post of his experience with lighting sharp contrast with the garish effect of light in painting ever"....
Mystery sign, you have beaten me, I do not honestly know

I could make out enough to realize that it's nonsense.

It says, "Dude, I'm a bad texture. Don't worry about reading me. From here on out I'm probably just going to spout nonsense."

Presumably about Alphonse Mucha?

Looks like it's not quite the best english.

To be fair, the "Spring Won't Come Vacation" part makes complete sense in context. You're out to rescue the seasons or whatever.

http://www.all-art.org/symbolism/mucha2.html