[Закрытые] Error displayed

Background of the issue:
I am trying to remove an error from my admin panel. The error message states that WPML String Translation is attempting to write .mo files with translations to the folder /var/www/ctt/wp-content/languages, which appears to be not writable. This is blocking translation for strings from appearing on the site. I have already tried the solution provided in this forum post: https://wpml.org/forums/topic/wpml-string-translation-is-attempting-to-write-mo-files-with-translations-to-fo-8/

Symptoms:
The error message 'WPML String Translation is attempting to write .mo files with translations to folder: /var/www/ctt/wp-content/languages. This folder appears to be not writable. This is blocking translation for strings from appearing on the site.' is displayed on my admin panel.

Questions:
How can I make the folder /var/www/ctt/wp-content/languages writable?
Why is the solution from the forum post not working anymore?