On the construction of fully interpreted formal languages which posses their truth predicates

We shall construct by ordinary recursion method subsets to the set $D$ of G"odel numbers of the sentences of a language $\mathcal{L}$. That language is formed by sentences of a fully interpreted formal language $L$, called an MA language, and sentences containing a monadic predicate letter $T$. From the class of the constructed subsets of $D$ we extract one set $U$ by transfinite recursion method. Interpret those sentences whose G"odel numbers are in $U$ as true, and their negations as false. These sentences together form an MA language. It is a sublanguage of $\mathcal{L}$ having $L$ as its sublanguage, and $T$ is its truth predicate.