In 5.11 we added a language override, under /language/xx_yy/_override.php, this file is renamed from _override-example.php. Setting an override here works fine for en_us, but if you copy the _override.php file into any other language directory, like /language/de_de/ or /language/es_es/ it has no affect when using that language.
To reproduce:
1. Install a language like es_es and select it for your staff user.
2. Copy _override-example.php to _override.php
3. Copy _override.php to the language directory like /language/es_es/
4. Edit the file and uncomment the 2nd example:
$lang['AppController.structure.text_settings'] = 'Configuration';
This controls the "Settings" link in the upper right corner of the admin area, to the left of Log Out. Note that the language remains the same. But, if you uncomment the line in /language/en_us/_override.php, the Settings link now shows "Configuration".