I'm not sure I understand the problem specification. You want to be able to search "law", and find documents containing "qanoon" or "kanun", right? How does your proposed solution handle that? It seems like the approach with ML TL -> Lucene would still only find one of the two, unless your model is written to return a set of possible transliterations. Or are you saying your approach doesn't currently solve this part of the problem, and that's one of the things you'd like input on?

Is the corpus the only data you have, i.e. do you need to use it for training and validation as well?

In terms of the size of the data, if you want to store the corpus on the phone anyway, won't the index and model be relatively small in comparison?