how can I translate the word by the plugin if I need to be logged out?
The same way as described above.
You can translate the plugin as described in the following pages.
https://wedevs.com/95777/translating-wordpress-plugins/
https://www.wpbeginner.com/wp-tutorials/how-to-translate-a-wordpress-plugin-in-your-language/
https://premium.wpmudev.org/blog/how-to-translate-a-wordpress-plugin/
Can you say me where I have to change the word in the plugin code?
It is added on line number 250 in the following plugin file.
/login-logout-register-menu/admin/class-login-logout-register-menu-admin.php
Please note you are making changes in the plugin files therefore you have to make these changes again after plugin updation as changes made in the plugin files get lost on theme updation.
Unfortunately I do not have to time to translate the entire plugin.
You don’t have to translate entire plugin. Just translate the strings that you want to change.