The airport scene makes no sense

I can't understand Danny DeVito's character in this movie, or anyone's actions or decisions.

So Joan Wilder arrives at the airport and proceeds to walk to the 'bus platform'. Now, WHAT did they arrange? How did they plan to meet? Was it:

1) Meet Danny (I'll just call him that for simplicity) at the airport, where the bus terminal/platform is and hand him the map, then we'll release your sister?

Would make NO sense for her to then board a darn bus to Cartagena, now would it? Why would she break the agreement that way? WHY would she go to Cartagena, if they are supposed to meet at the airport?

2) Meet at Cartagena, give Danny the map, they will release your sister?

Would make NO sense for Danny to then come all the way to the Whatever (I can't be bothered to check out) Airport to meet her, if he KNOWS she's going to go to Cartagena before even expecting to meet anyone, now would it? WHY would Danny go to the Airport, if the arrangement is to meet in Cartagena?

You see how this whole thing makes no sense...?

Also, as a bonus item - HOW the heck would she need a dictionary to ask where the bus is going? Just say the name 'Cartagena', which she doesn't have to try to read from some book, because she already knows the name, and thus how to pronounce it - how else would she know to ask about it?

But there's more... WHAT kind of a dingbat does she have to be to NOT check the upper front of the bus for the destination? THIS IS A UNIVERSAL CONCEPT, it works in pretty much EVERY SINGLE COUNTRY that has buses that go somewhere... can you name one country where buses DO NOT display the destination above the windshield or somewhere in the front, usually upper side?

How.. would .. she.. NOT .. know.. to.. check.. there..??

Also, why would that bus have 'Cartagena' printed on that plate, but then someone comes and switches it around? Is that the bus driver? Why would they have to sit on the roof to change that plate, isn't there a less cumbersome way? I can't believe the bus driver would climb all the way up there to change it every time!

My point is, if it's not going to Cartagena, why does the plate say 'Cartagena' before someone flips it around? I mean, if it just came from some place, it would say 'Whatever Airport' as the destination, right? If it's not going to Cartagena, the plate should already be correct, right? I mean, wouldn't they make sure at the stable before leaving for the airport that they have the correct destination printed on the plate? Otherwise they might have the WRONG PLATE altogether, and this guy just turning it around doesn't necessarily show the correct destination, and the bus driver doesn't even CHECK it?! What kind of a bus driver is this?

Also, why doesn't ANYONE correct the 'evil guy', when he lies to her and say 'This bus is not going to Cartagena, what are you talking about?' (Obviously in spanish probably though)

Also also also also, why can't she just simply confirm with the bus driver before the bus leaves, not after like 2 hours of driving? Why doesn't the bus driver understand what she's asking, when bus drivers should EXPECT people to be asking about destinations all the time, so even though she's pronouncing it weirdly and using an american accent, the bus driver should surely still know what the heck is being asked...

Yeah, great classic movies don't make sense any more than the newest marvel crap, they just have the wonderful 1980s atmosphere and music to distract you from that.. well, among other things.