The strings you’ve mentioned are localized. You can check the file /app/Locale/nl_NL/translations.php, line 473
'%dd' => '%dj',
Days in Dutch is Dagen? Do you use the letter ‘d’ to abbreviate it?
You can do a search in this file to fix/add any other strings and then make a Pull Request so it will be fixed to everyone on next version. Until then, you may edit this file on your kanboard instance to get it fixed for you.
If you don’t know how to make a pull request I may assist you or do it for you, if you provide the correct texts.