The text has apparently been modified over the years, but I don't know to what extent...
Here is the same image, the first version is from the 1930 edition and the second one is from the 1946 edition:
First picture:
Tintin: "My dear friends, I will talk to you today about your fatherland: Belgium!"
Second picture:
Tintin: "If you agree, we will start with a few arithmetic operations. Who can tell me how much is 2 + 2 ? Nobody?... Come on, 2 + 2 ?... 2 + 2 = ...?"
I have no idea what it says nowadays... It probably has not changed much, because I think the main story stayed the same...