Currently, the back button title is replaced with "Back" only when the previous route title is longer than 12 characters, which doesn't seem to match the native iOS logic.

The attached screenshots demonstrate how native iOS navigation bar replaces the previous route title only when there's not enough room to fit the title.

A common parent route:

Back button title is "Back" instead of "Keyboards" since there's not enough room to fit it:

Back button title is "Keyboards" since there's enough room to fit it:

Flutter version:

Flutter 1.9.1+hotfix.2 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 2d2a1ffec9 (9 days ago) • 2019-09-06 18:39:49 -0700
Engine • revision b863200c37
Tools • Dart 2.5.0