how to add custom transliteration mapping

using the qwerty keyboard for phonetics sometimes does not bring the relevant word and requires switching to native keyboard to get the word right but then that word does not get save making it impossible to teach new words to the phonetic keyboard. For instance:

• The word "chappal" when typed does not provide a meaningful prediction in Hindi - ideally it should provide predeiction "चप्पल ".
• Typing "ch" only provides "छ" and no option for "च"

Now this would be reasonable so long as user had some way to map the phonetic predictions. Is it possible or is it on the roadmap as a feature?