Keyboards for Hinglish and Other Romanized Languages of India
Users of the languages of India sometimes prefer to type with keyboards that produce Romanized versions of these languages (for example "Hinglish") instead of with native script or transliteration input systems. iOS used to have a keyboard called "India (Latin)" for this.
iOS 18 offers a new bilingual keyboard feature which can be used to create such keyboards for Hindi, Bangla, Gujarati, Marathi, Punjabi, Tamil, and Telugu.
First add English (India) to your list in Settings > General > Keyboard > Keyboards
Then tap on English (India) and then on Add Language.
Choose what language you want to add to English (India). The end result will be a keyboard with a double name, such as "English (India) & Hindi", which you can make active via the Globe key.
I don't know how well any of these work. Feel free to comment on that.