1. A computer-implemented method of assessing non-native speech proficiency, comprising: processing, using a processing system, a non-native speech sample to identify a plurality of vowel sound boundaries in the non-native speech sample; analyzing, using the processing system, portions of the non-native speech sample within the vowel sound boundaries to extract vowel characteristics; processing, using the processing system, the vowel characteristics to identify a plurality of vowel space metrics for the non-native speech sample; and processing system, using the processing system, the vowel space metrics to determine a non-native speech proficiency score for the non-native speech sample.