The so-called 'strong form' of this hypothesis
is that one cannot think
which cannot be expressed
in one's language
. The weaker form states that it is easier to think thoughts which are easily expressible in one's language, and conversely, harder to think thoughts which are not easily expressed.
While it is true that most scholars reject the strong form, it might be more accurate to state that the strong form is not even wrong. The weak form is still hotly contested by a number of factions in psychology, linguistics and philosophy. Whether or not one believes this hypothesis is correct is probably strongly correlated with one's beliefs about whether language is innate or learned.