Steps to reproduce:

1. Install or upgrade to 5.0dev (Build: 20241122) or  It includes MDL-83226
2. Install another language pack (for example PT-PT Portugal)
3. Make sure you have updated all language packs
4. As a admin,go to General backup defaults.
5. Change language to PT-PT
6. Verify that exists the option "Include custom fields"
7. Enable &strings=1 in URL of the page and verify that you have backup | backup_general_customfield and {configgeneralcustomfield/backup}
8. Go to AMOS (https://lang.moodle.org/local/amos/view.php)
9. Select Standard and search for string in String identifier: configgeneralcustomfield, configrestorecustomfield, generalcustomfield
10. Make sure you have selected version 5.0 or 4.5
11. No such strings found.

Same happens in version 4.5