prediction only works in Calendar but not in Message application.
That is not prediction but rather a completer.
I don’t understand what do you mean by “reference input”
Some explanation on the topic: Jolla licensed a predicitive engine called Xt9 from Nuance and this is what they ship to the Jolla1/C/AquaFish and Xperia X licensed customers. However this prediction engine does not support the community supported languages and not available for the non licensed SFOS installations i.e. ports.
So we decided to hack our own prediction plugin based on the presage library.
It has several predictors the most important is the ngram predictor.
This works roughly the following way: we grab a large amount of text which contains a representative sample from the words/phrases used in a given language. This is what called corpus. For some languages there are available corpuses usually maintained by universities, however some does not have such available. For e.g for Hungarian I used some novels, and some polite letters which is somewhat working but not ideal.
To install the language support for the predictor this corpus got sliced to ngrams. ngram are basically two-three-four word chains extracted from the corpus. These ngrams are put to a database and the predictor make suggestions based on the ngrams matching your last typed words.
Large ngram sets makes the queries slow so the good corpus should be small (while still representative).