I've used Icelandic as a secret language. I think it works pretty well (just as long as you're not, you know, in Iceland) I've had the most success with it in the US. A lot of people there don't know Icelandic exists and I've had people ask me why I'm writing things in Elvish before.
Also the guy I met is friends with like all the Canadians in Kyoto, so I think it might be a thing that Finnish people automatically get all the Canadians. I'm starting to see a pattern. He even called Finland "The Canada of Europe".
Icelandic and Finnish both work as secret languages even within the countries if you have a thick enough an accent, I had a rough first year here of absolutely no one understanding me.
Also reminds me of some movie, the name escapes me but the characters used Finnish as a secret language, only the pronunciation was so far off that you only realized it happening if it was pointed out.
Well... we're also in the north and like ice hockey but to be honest we never apologize for anything and you can't exactly call Finns "polite", no matter which way you try to look at it.
On another topic, today's going to be just rivets, rivets, rivets. I've only got a bit over a hundred of them in and my fingers already hurt, this is probably the most I've bled on a cosplay ever. Besides I'm also having painful flashbacks to my youth as a mopey punk to add insult to the injuries...