Consider the second statement of B - I do not always speak the truth.
A truth-teller won't say this statement. Even a liar won't say this statement. Hence, B must be an alternator. And this statement is true. Hence, B's first and third statements must be false.
B's first statement is that A is a liar. Hence, A is not a liar. He must be a truth-teller or an alternator.
B's third statement is that he knows French, which is false.
A's second statement is that B knows French, which is false, hence, A must be an alternator. Hence, his first and third statements must be true.
Hence, C is from Australia.
Also, D is a liar or an alternator.
Let us analyse D's statements.
The second statement of D is:
There is only one liar.
We know that A and B are not liars. Hence, if this statement is true, then C is the only liar and D is the alternator. If this statement is false, since there must be at least one liar, in this case, both C and D are liars.
Since we know that in both cases, C is a liar, we can analyze his statements.
D is from Europe since C is a liar.
Also, A is from Asia and A speaks Spanish.
B must be from Africa.
A who is an alternator says that B knows French as his second statement, which is false.
We know that the first and third statements of D are false since he is a liar or an alternator(with the second statement true). Hence, D does not speak French.
B must be from Africa.
Hence, we get the following 2 arrangements.
If German is spoken by a liar, it corresponds to the first case, we can simplify the table as:
Hence, 2 statements of A are true and one statement of B is true. So, a total of 3 true statements are spoken.