I think there is something wrong in this understanding of understanding. Claiming understanding is translation seems to impliy that everything can be compared in some universal reading grid. However understanding has to happen in subjective contexts, or reading grids. Sense happens through the choice of a point of view, which may not be comparable to another. The subjectivity means that translation has to be interpretation, therefore it can't be the whole story.
In particular I would say that this idea lacks the fact that translations may not be relevant; and that what is good translations may not even be knowledgable. These aspects of translation by the way do not seem to be understandable in terms of translation