short_description.txt: update source and translations (attempt 2)

Inspiration from https://jami.net/ with text:
Share, freely and privately

Follow up to:
https://review.jami.net/c/jami-client-android/+/30234
https://review.jami.net/c/jami-client-android/+/29841

Hopefully show on the Google Play Store as one line.
For English, use sentence case (except for proper nouns)
Generally sentence ends without a period.
A short description should convey your app or game's message in 80 characters or less.
https://support.google.com/googleplay/android-developer/answer/13393723

https://support.google.com/googleplay/android-developer/answer/9844778?visit_id=638743605084629665-1079397603&rd=1#zippy=%2Cview-list-of-available-languages

Change-Id: I2a0137b420ca9bc44208cf426e72ae1ed43b73de