The natural language is the infinite level, the container of the formal languages. If the container goes, everything goes. And this container, this infinite level language, must include its own semantics. In summary, the crucial assertion is the assertion that there is language, made in the natural language. This assertion is true if it is meaningful.
Beliefs stand or fall on the question of whether there is language.
There is no way to get outside the definitional trick and ask this question in a way that would be substantive. The question simply collapses.