Can an electrical breaker panel be inserted on an exterior wall, inside the house, or is it required that it is on an interior wall, inside the house?
They are almost always on an exterior wall. In some areas they are on the outside of the exterior wall - outside your house. Most inspectors would tell you that a garage (interior or exterior wall) or in the basement exterior (right where the line comes in) are the two best locations.
If you are having questions on where your panel should be your local city building inspector will surely give you a couple minutes.
The National Electric Code only requires the fist disconnecting means to be either on the outside of the building or within the closeset point of entrance. In Chattanooga our inspectors have adopted the requirement that the service disconnecting means that is inside that it cannot be over 5ft from the entrance of said cable or wires. If your service entrance wires are buried and come in the building in the middle of of the structure it shall be no further than 5ft to disconnecting means.
Here in Canada (Ontario and Manitoba) I have never seen a service panel mounted on the outside of a house. I would think this is self-evidently undesirable, as any random person walking by outside could wreak havoc, from merely switching off some circuits to stealing breakers or even opening the panel and disturbing the wiring. Also, needing to go outside in -40˚C weather to diagnose a tripped breaker is no picnic.
It is, however, common, to have the meter base on the outside of the house, feeding a service panel on the inside of the house. The service panel must be close to the meter base in many municipalities, although some allow longer runs of suitably-sized conduit to carry load-side service conductors from the meter base to a service panel inside the house, which is done if the meter base is located on the outside wall of a garage, for example.