11. A system for assessing the pronunciation difficulties of a non-native speaker comprising: a processor; and a processor-readable storage medium in communication with the processor, wherein the processor-readable storage medium contains one or more programming instructions for causing the processor to perform a method of predicting the pronunciation difficulties of a non-native speaker, the method comprising: determining a plurality of different types of phonetic sources of pronunciation difficulties between a language of a non-native speaker and a second language, said determining including determining multiple types of sounds in the second language that cause pronunciation difficulties; assigning a weight to each phonetic source of pronunciation difficulty, the weight representing a measure of severity of the source of pronunciation difficulty; calculating a phonetic difficulty score, wherein calculating the phonetic difficulty score comprises calculating a product of a number of times the phonetic source occurs in an utterance of the non-native speaker and the weight of the phonetic source; calculating a language model score based on a sound comparison between the language of the non-native speaker and the second language, wherein the language model score is calculated based on a difference between a cross-entropy of the utterance with respect to a language model of the language of the non-native speaker and a cross-entropy of the utterance with respect to a language model of the second language; normalizing the phonetic difficulty score and the language model score; and calculating and outputting a metric from the normalized phonetic difficulty score and the normalized language model score, the metric providing an assessment of pronunciation difficulty.
11. A system for assessing the pronunciation difficulties of a non-native speaker comprising: a processor; and a processor-readable storage medium in communication with the processor, wherein the processor-readable storage medium contains one or more programming instructions for causing the processor to perform a method of predicting the pronunciation difficulties of a non-native speaker, the method comprising: determining a plurality of different types of phonetic sources of pronunciation difficulties between a language of a non-native speaker and a second language, said determining including determining multiple types of sounds in the second language that cause pronunciation difficulties; assigning a weight to each phonetic source of pronunciation difficulty, the weight representing a measure of severity of the source of pronunciation difficulty; calculating a phonetic difficulty score, wherein calculating the phonetic difficulty score comprises calculating a product of a number of times the phonetic source occurs in an utterance of the non-native speaker and the weight of the phonetic source; calculating a language model score based on a sound comparison between the language of the non-native speaker and the second language, wherein the language model score is calculated based on a difference between a cross-entropy of the utterance with respect to a language model of the language of the non-native speaker and a cross-entropy of the utterance with respect to a language model of the second language; normalizing the phonetic difficulty score and the language model score; and calculating and outputting a metric from the normalized phonetic difficulty score and the normalized language model score, the metric providing an assessment of pronunciation difficulty. 17. The system of claim 11 , wherein the multiple types of sounds in the second language that cause pronunciation difficulties include: a first sound that does not contrast with a second sound in the language of the non-native speaker; and a third sound that does not exist in language of the non-native speaker.