Conversation

Skype is shutting down in May. I've been using it to speak with my grandmother, and I am looking for an alternative, with the following features:
* can do live subtitles (in French)
* works without a phone number/sim card
* can call your contacts and be dialed (i.e. not only invite by email/calendar/url…)
* simple UI/UX (with big buttons) is far more important than feature rich.

I know various things that do some of the above, but I'm not sure what (other than Skype) does all of it.

Any help?