1. An apparatus for generating at least one phonetic pronunciation for an input sequence of letters selected from a predetermined alphabet, comprising: a memory for storing a plurality of letter-only decision trees corresponding to said alphabet, said letter-only decision trees having internal nodes representing yes-no questions about a given letter and its neighboring letters in a given sequence; said memory further storing a plurality of mixed decision trees corresponding to said alphabet, said mixed decision trees having a first plurality of internal nodes representing yes-no questions about a given letter and its neighboring letters in said given sequence and having a second plurality of internal nodes representing yes-no questions about a phoneme and its neighboring phonemes in said given sequence, said letter-only decision trees and said mixed decision trees further having leaf nodes representing probability data that associates said given letter with a plurality of phoneme pronunciations; a phoneme sequence generator coupled to said letter-only decision tree for processing an input sequence of letters and generating a first set of phonetic pronunciations corresponding to said input sequence of letters; a score estimator coupled to said mixed decision tree for processing said first set to generate a second set of scored phonetic pronunciations, the scored phonetic pronunciations representing at least one phonetic pronunciation of said input sequence.
1. An apparatus for generating at least one phonetic pronunciation for an input sequence of letters selected from a predetermined alphabet, comprising: a memory for storing a plurality of letter-only decision trees corresponding to said alphabet, said letter-only decision trees having internal nodes representing yes-no questions about a given letter and its neighboring letters in a given sequence; said memory further storing a plurality of mixed decision trees corresponding to said alphabet, said mixed decision trees having a first plurality of internal nodes representing yes-no questions about a given letter and its neighboring letters in said given sequence and having a second plurality of internal nodes representing yes-no questions about a phoneme and its neighboring phonemes in said given sequence, said letter-only decision trees and said mixed decision trees further having leaf nodes representing probability data that associates said given letter with a plurality of phoneme pronunciations; a phoneme sequence generator coupled to said letter-only decision tree for processing an input sequence of letters and generating a first set of phonetic pronunciations corresponding to said input sequence of letters; a score estimator coupled to said mixed decision tree for processing said first set to generate a second set of scored phonetic pronunciations, the scored phonetic pronunciations representing at least one phonetic pronunciation of said input sequence. 13. The apparatus of claim 1 further comprising a language learning system that displays a spelled word and analyzes a speaker's attempt at pronouncing that word using at least one of said letter-only decision tree and said mixed decision tree to tell the speaker how probable his or her pronunciation was for that word.