1. A computer-implemented method of generating recitation items for assessing speaking proficiency, the method comprising: generating, using one or more processing systems, one or more text sets, wherein each text set is in a target language and includes one or more texts; extracting a target language phoneme distribution from a target language corpus that is in the target language; extracting a first native language phoneme distribution from a first native language corpus that is in a first native language of one or more users; extracting a second native language phoneme distribution from a second native language corpus that is in a second native language of one or more users; comparing the target language phoneme distribution to the first native language phoneme distribution to identify any first phoneme n-gram (i) whose frequency of appearing in the target language corpus satisfies a first predetermined criterion and (ii) whose frequency of appearing in the first native language corpus satisfies a second predetermined criterion, wherein any such identified first phoneme n-gram is included in a first list; and comparing the target language phoneme distribution to the second native language phoneme distribution to identify any second phoneme n-gram (i) whose frequency of appearing in the target language corpus satisfies a third predetermined criterion and (ii) whose frequency of appearing in the second native language corpus satisfies a fourth predetermined criterion, wherein any such identified second phoneme n-gram is included in a second list; determining, using the one or more processing systems, a value for each text set using one or more metrics that include a phonetic difficulty metric by: generating phoneme sequences for each text set; comparing the phoneme sequences with a phonetic challenge list that includes any phoneme n-gram appearing in both the first list and the second list; computing, based on the comparison, a respective phonetic difficulty value for each text set, and determining the value for each text set based on at least the respective phonetic difficulty value; and selecting, using the one or more processing systems, a final text set from the one or more text sets to serve as the recitation items for assessing speaking proficiency based on the values associated with the text sets.