riddle - Treasure hunt 'round the world! (clue 1)

If you're interested in starting the treasure hunt from the very beginning, check out the prologue!

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After mailing in the correct question to the given answer in the preliminary test, it took only a couple of days to receive your actual invitation to participate in the Treasure Hunt 'Round the World. You eagerly tear into the gaudy, glittery envelope and read the letter enclosed:

Dear [insert username here],

Congratulations on your acceptance into the Treasure Hunt 'Round the World! Prepare yourself for a steeling worldwide adventure, where you will be pushed to your vastest limits in pursuit of the coveted treasure! I hope you've packed your bags, because the race... starts... NOW! Your itinerary is enclosed. Good luck, racer!

Yours truly,

Bailey M

Puzzlemaster for the Treasure Hunt 'Round the World

P.S. When you arrive at the departure airport, members of our team will be there to assist you in searching for the fastest flight and booking your ticket.

You rummage through the envelope hurriedly, pulling out the itinerary. On it, you read:

Your flight departs at 1:47 from the Pocatello Regional Airport.

Your destination is:

The 63rd member, periodically;
a butterfly's sway, unconditionally,
with common tongue tied to no other,

spoken unlike their American brother
(though the two decline unanimously).

Once you've found the desired country,
your flight will arrive at 2:53.

Luckily, you did already pack your bags! Time to get racing!

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What airport are you departing from, and what city are you flying into?

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Per the request of Aggie Kidd, here's a nod in the right direction, based on each line:

Your flight departs at 1:47 from the Pocatello Regional Airport.

The answer to this may be a bit trivial, since there have been so many good responses already, but none of them are exactly what I was looking for. Everyone's on the right track. As a hint, you are departing from North America, and Pocatello's airport code is not actually used in the puzzle.

The 63rd member, periodically;

There is a way to interpret the answer to this line a bit more specifically, which will significantly narrow down the number of possible countries.

a butterfly's sway, unconditionally,

I believe this was solved rather innocuously in the comments of an answer.

with common tongue tied to no other,

This line has not been interpreted as intended yet. The most common language in the destination country is also the most common language in other countries.

spoken unlike their American brother

This line has been interpreted correctly, though the country has not been correctly identified.

(though the two decline unanimously).

I believe rand al'thor correctly picked this one out, which should give you some guidance.

Once you've found the desired country, your flight will arrive at 2:53.

This is unsolvable without first having the country name.

Also a general hint about how to solve this puzzle: When I was creating it, I made a blanket list of all possible countries, then started whittling them down, clue by clue, until I had one remaining. If I had to solve this puzzle, I would try to do the same.

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The story continues in the next part, Treasure hunt 'round the world! (clue 2)

Answer

Partial answer

Your flight departs at 1:47 from the Pocatello Regional Airport.

Take the 1st letter of Pocatello, the 4th letter of Regional, and the 7th letter of Airport to get PIT. Interpreting that as an airport code, it looks like we're flying out of Pittsburgh International Airport.

The 63rd member, periodically;

63rd on the periodic table is Europium, with chemical symbol Eu, so we're heading for somewhere in the EU (European Union).

a butterfly's sway, unconditionally,

Unconditional sway suggests monarchy, and the Monarch Butterfly is a common butterfly species in North America.

with common tongue tied to no other,
spoken unlike their American brother
(though the two decline unanimously).

So we want a monarchy in the EU with a common language not spoken in any other country, similar to a language spoken somewhere in the Americas, the word for "no" being the same in both languages. Let's try Spain (taking Latin American Spanish to be a separate language, as some do consider it to be).

Once you've found the desired country,
your flight will arrive at 2:53.

As with 1:47, we take the 2nd, 5th, and 3rd letters of SPAIN to get PNA, which is the airport code for Pamplona Airport.

So our destination city is

Pamplona, Spain.