@asti This is not an error that requires an admin login. It's easily reproducible on a vanilla WordPress install running the latest version of WordPress and the WP Discuz plugin. Make sure you enable WP_DEBUG and then review the logs and access any page. I reviewed your plugin and there are numerous files that try to process translations too early which are causing this notice.
For example, in wp-content/plugins/wpdiscuz/options/class.WpdiscuzAddons.php, in your __construct() you run...
This method then uses esc_html__() such as...
"desc" => esc_html__("All 16 addons in one bundle. Save 90% and get Unlimited Site License with one year premium support.", "wpdiscuz"),
However, you cannot run translation methods this early which in the case of that construct it's before `after_setup_theme` or `init`. Per the WordPress doc I linked earlier...
When attempting to load translations before after_setup_theme or init, WordPress tries to load the current user earlier than usual, without giving other plugins a chance to potentially hook into the process. It also prevents any plugins from filtering translation calls, e.g. for switching the locale or file location. Hence the addition of this warning to call out this unexpected behavior.
This early use of translations is what is causing the notice and should be fixed. Your logic needs to be refactored to set/translate the text later.
Let me know if you need any further information to try and reproduce on your end.