Hi Memotas,
If your website not a multilingual then it is easier to use language override. Most of all wordings you mentioned above can be changed from the backend, so you don't need to touch any file changes manually
(like, duplicating the language files, translating it and then uploading it).
The reason why we didn't put those wordings above into language files because for most users it is easier to change those wordings from the backend, without touching the code.
Exception for these wordings :
11-A new offline message from (For Mail Form)
12-You received a message from (For Mail Form)
We have tried it before, but unfortunately Joomla always send the language strings untranslated, that's why we leave it hardcoded.