@PitaJ No errors, I redid it from scratch and it worked, I must have done something wrong. Thank you.

Hi,
I need to replace the value of error:email-not-confirmed-email-sent.
In plugin.json I added "languages": "languages" entry.
Polish is my language configuration so in languages/pl/error.json I added corresponding entry "email-not-confirmed-email-sent": "NEW_VALUE".
I rebuild and restart nodebb and still the old value is shown.
Is it possible to replace core language key values with plugins?