No data is collected for storage or shared at all.
App doesn't have internet permission.
Accessibility feature that allows you to convert/transliterate text on screen requires text from the app to be processed. But this data is not stored or shared at all. The accessibility feature is also optional and requires explicit consent from you.
The app is open source. You or a software developer can verify the source code at https://github.com/subins2000/manglish