5. A non-transitory storage medium storing instructions executable on a digital processor to perform a method including (i) translating source language content in a source natural language to a target natural language based on a conditional translation probability conditioned on the source language content and (ii) tuning the conditional translation probability using a translation pool, wherein the tuning includes: selecting candidate aligned translations for a source language sentence having a reference translation by sampling available candidate aligned translations for the source language sentence in accordance with the conditional translation probability conditioned on the source language sentence; wherein the conditional translation probability for a translation (e,a) of source language content f is monotonically increasing with exp ⁡ ( ∑ k = 1 K ⁢ λ k ⁢ h k ⁡ ( e , a , f ) ) where h k (. . .), k=1, . . . , K denotes a set of K feature functions and λ k , k=1, . . . , K denotes tuning parameters of the conditional translation probability; wherein the selecting comprises: constructing a translation lattice representing the available candidate aligned translations for the source language sentence; and sampling the available candidate aligned translations by sampling paths through the translation lattice from its root node to its final node wherein each transition from a current node to a next node is selected based on conditional translation probabilities σ ⁡ ( e i ) = ∑ k = 1 K ⁢ λ k ⁢ h k ⁡ ( e i ) of the available edges e i leading away from the current node, and adding the selected candidate aligned translations to the translation pool.
5. A non-transitory storage medium storing instructions executable on a digital processor to perform a method including (i) translating source language content in a source natural language to a target natural language based on a conditional translation probability conditioned on the source language content and (ii) tuning the conditional translation probability using a translation pool, wherein the tuning includes: selecting candidate aligned translations for a source language sentence having a reference translation by sampling available candidate aligned translations for the source language sentence in accordance with the conditional translation probability conditioned on the source language sentence; wherein the conditional translation probability for a translation (e,a) of source language content f is monotonically increasing with exp ⁡ ( ∑ k = 1 K ⁢ λ k ⁢ h k ⁡ ( e , a , f ) ) where h k (. . .), k=1, . . . , K denotes a set of K feature functions and λ k , k=1, . . . , K denotes tuning parameters of the conditional translation probability; wherein the selecting comprises: constructing a translation lattice representing the available candidate aligned translations for the source language sentence; and sampling the available candidate aligned translations by sampling paths through the translation lattice from its root node to its final node wherein each transition from a current node to a next node is selected based on conditional translation probabilities σ ⁡ ( e i ) = ∑ k = 1 K ⁢ λ k ⁢ h k ⁡ ( e i ) of the available edges e i leading away from the current node, and adding the selected candidate aligned translations to the translation pool. 6. The storage medium as set forth in claim 5 , wherein the tuning employs the bilingual evaluation understudy (BLEU) method.