Hindi vs Hinglish: what people actually speak
Hinglish is not broken Hindi. It's how most bilingual families in India (and abroad) talk every day: Hindi grammar as the skeleton, English words dropped in wherever they feel right. If you're learning Hindi to talk with a partner's family, you're mostly learning Hinglish.
Same idea, three flavors
Why textbooks skip Hinglish
Textbooks teach the version you'd write in a formal letter. Families don't write formal letters at dinner. They say "thoda water do", not "thoda paani dijiye", and both are correct.
What Bolo does differently
The phrases in the app are the ones people actually say. When a family really would use the English word ("weekend", "office", "biryani"), the app keeps it. When Hindi is warmer or clearer, the app uses that.
When to switch to full Hindi
Grandparents, formal introductions, and religious moments usually want the full-Hindi version. Everywhere else, Hinglish reads as natural and respectful. If you're unsure, mirror whatever the room is speaking.