The Kunena team has announce the arrival of Kunena 6.2.5 [K 6.2.5] which is now available for download as a native Joomla extension for J! 4.3.x/4.4.x/5.0.x. This version addresses most of the issues that were discovered in K 6.1 / K 6.2 and issues discovered during the last development stages of K 6.2
Go in backend to "Extensions > Language(s) > Overrides > (Filter)-Site > New". Enter in the field Language Constant this code:
COM_KUNENA_NO_ACCESS
Enter your new text in the text field and save it.
Again "Overrides -> (Filter)-Administrator > New"
COM_KUNENA_ACCESS_DENIED
and enter your new text
That's all.