> It will be very helpful if someone come up with automatic tonal detection systems for language learners to automatically check the correctness of their pronunciations […]
The number embedded in the Jyutping pronunciation indicates the tone.
However, the automatic tonal detection is not as straightforward as it might seem due the tone sandhi (the tone change of the word/syllable depending on surrounding morphemes), and not all tonal languages have the tone sandhi. Cantonese, Teochew and Hokkien languages can have a pretty complex tone sandhi, though.
For Cantonese and Jyutping specifically, the tone sandhi is marked as, e.g., «faan4*2» which means that the standard pronunciation is «faan4» (the low falling tone) can change into «faan2» (the high rising tone) depending on the following morpheme. The tone sandhi does not have fixed rules and depends on each morpheme. Depending on the tonal language, the preceding morpheme can initiate a tone change, or it can be the following one. Certain tonal languages can have a complex tone sandhi that affects the tonal change not just in a single morpheme but it the rest of the morphemes that comprise a full word.
We would really be talking about a full contextual, semantics aware automated translator that applies the approriate tone sandhi on the contextual basis to give a Western reader the correct tone rendition in the transliteration.*