It says: "Merkje det sted um mannen han stupe" "Nystua" "Innviet av kronprinsesse Martha"

It's written in old Norwegian or, more directly, an older version of "New Norwegian". Which is a miss-leading name, as it's the oldest "version", a "true" version of what Norwegian used to be, before the Danish rule and the Danish-Norwegian union. Either way, "Merkje det sted um mannen han stupe" is a quote from a poem written by Per Sivle, first published in 1885. It says "mark this place, for this is the place that the man(king, sacrifice) died". This translation is a longer, but more explanatory than what it says. The poem, from what I can understand, is a description and retelling of the The Battle of Stiklestad.

The second line "Nystua" is probably the name of the place(the room which it's in). Ny=new, Stua=living-room, so new-living room. Stua in Norwegian has more than just the one meaning, it is used to describe a place where one gather, usually indoors, as a larger or more official "living-room", think of it as how you'd use "hall or quarters" in a way. But "stua" can also be used to describe any old living room.

The third line says who it was inaugurated or consecrated there by. As in this case, the Crow-Princess Martha. She was the Norwegian-Swedish Crown-Princess, mother of the ruling monarch of Norway, Harald V of Norway.

I hope this suits your needs. If you care to read the poem in question, have at it, Link