Speech-To-Text apps

Hi!

My grandma is having trouble hearing (she is almost deaf), and it's getting really hard to communicate with her. I wanted to give her an app (preferably a smartphone) which does Speech to Text in real time so she can read what we are trying to say to her.

I've been searching for a few days, but I couldn't find anything useful, it's like there isn't a lot of people needing something like this (just leave your phone on and it will display whatever the other person is saying).

Please help :)

These are the features I'm looking for:

• Spanish support (my grandma only speaks spanish).
• Offline (we want it to be available on the go, we don't have 4g in our country).
• Real Time (just for convenience, always listening).