Full Idea
If the definition of the truth predicate is to be finite (Tarski insisted on this), the definition must take advantage of the fact that sentences, though potentially infinite in number, are constructed from a finite vocabulary.
Gist of Idea
The language to define truth needs a finite vocabulary, to make the definition finite
Source
Donald Davidson (The Folly of Trying to Define Truth [1999], p.23)
Book Reference
Davidson,Donald: 'Truth, Language and History' [OUP 2005], p.23
A Reaction
Not sure whether this is in the object language or the meta-language, though I guess the former.