Assuming the winds directed a hot air balloon near a US international airport, and the pilot has no other choice than landing, say near the runways/taxiways, would they face legal trouble/fines?
Assuming the winds directed a hot air balloon near a US international airport
By this I assume you mean a major airport in class B or C (possibly even D) airspace. An "international" airport is simply one that is an airport of entry and maintains customs officials and processing ability and may or may not be a "large/major" airport.
would they face legal trouble/fines
This depends on how the balloon is equipped. As mentioned in the comments you need a transponder and a 2 way radio to enter certain controlled airspaces (usually those surrounding big airports) and if the balloon is properly equipped it would be allowed to enter and utilize public resources such as airports and landing areas. This advisory circular on ballooning would indicate it is legal to enter all airspaces in a balloon.
There are of course some practical problems here such as the fact that as a balloon you can't really divert around an airspace if you are not granted clearance. If there is no safe landing space and the wind is blowing such that your only option is to enter the class B you may be stuck declaring an emergency, or at least getting back on the radio and explain whats going on. Some FAA officials may consider this poor/dangerous flight planning (since you should have looked at the wind prior to departure) and you may end up in some trouble for that.
As a general rule, balloons do not freely operate within Class B airspace. Equipment requirements are the same as for Class C airspace; however, due to air traffic congestion, the balloon pilot requesting entry to Class B airspace will likely be denied entry, as ballooning operations inside the Class B airspace constitute a potential traffic conflict....
But legally you can and the FAA prefers you coordinate before hand,
Should it become necessary for operational reasons to fly through Class B airspace, that flight should be coordinated at least one hour prior, as provided for by 14 CFR section 91.215. It is permissible, and perfectly legal, to operate a balloon under the lateral limits of the Class B airspace.
Same applies for class C,
Balloon operations in Class C airspace, while technically feasible, are usually not advisable
What you are describing sounds like an emergency. In an emergency a pilot can take any reasonable actions necessary to ensure the safety of aircraft and occupants.
As others have mentioned there might be some other reasons for legal action, but since your question only refers to the landing of a balloon at an international airport, I will assume no other regulations were violated.
So, if no other regulations were violated up to the point that the balloon pilot had "no other choice" but to land at an international airport, then I would argue that the pilot could avoid (legal trouble/fines) either with a clearance from the tower(unlikely), or a declaration of an emergency.
A balloonist always has a choice of when he can land. He must carry enough fuel on board to remain aloft until a safe landing area can be reached. There is no way a busy control tower would allow him to land in the middle of the airfield. He might be granted clearance to fly through the control zone but would never be given clearance to land. If he was out of fuel, he would declare an emergency and accept the consequences. (Legal trouble/fines)