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The language of treaties, like that of any law or contract, must be interpreted when the wording does not seem clear or it is not immediately apparent how it should be applied in a perhaps unforeseen circumstance. The Vienna Convention states that treaties are to be interpreted "in good faith" according to the "ordinary meaning given to the terms of the treaty in their context and in the light of its object and purpose." International legal experts also often invoke the 'principle of maximum effectiveness,' which interprets treaty language as having the fullest force and effect possible to establish obligations between the parties.

Besides unclear language what might also arise that necessitates the interpretation of the language of a treaty?
a perhaps unforeseen circumstance