Which version of PHP GD Security Toolbox Pro plugin requires?
GD Security Toolbox Pro plugin requires one of the following PHP versions: 7.0, 7.1, 7.2, 7.3, 7.4, 8.0. The plugin might work with older PHP versions, but they are no longer tested or supported.
Which version of WordPress GD Security Toolbox Pro plugin requires?
GD Security Toolbox Pro plugin requires one of the following WordPress versions: 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6. The plugin might work with older WordPress versions, but they are no longer tested or supported.
Which version of ClassicPress (WordPress fork) GD Security Toolbox Pro plugin requires?
GD Security Toolbox Pro plugin requires one of the following ClassicPress versions: 1.0, 1.1, 1.2.
Which version of bbPress plugin GD Security Toolbox Pro plugin requires?
GD Security Toolbox Pro plugin requires one of the following bbPress plugin versions: 2.5, 2.6.
How old is GD Security Toolbox Pro plugin?
GD Security Toolbox Pro plugin is 5 years, 7 months old.
When was GD Security Toolbox Pro plugin first version released?
GD Security Toolbox Pro plugin was first released on March 16, 2016.
When was GD Security Toolbox Pro plugin latest version released?
GD Security Toolbox Pro plugin latest version 2.8.1 was released on April 20, 2021.
Where can I find list of changes in all GD Security Toolbox Pro plugin releases?
The detailed changelog for GD Security Toolbox Pro plugin is available here: GD Security Toolbox Pro Changelog.
Can I translate GD Security Toolbox Pro plugin to my language?

Yes. POT file is provided as a base for translation in the root folder for each plugin. Translation files should go into languages directory, and WordPress must be set to your language to load the file. As an alternative, translation file can go into wp-content/languages/plugins directory.

The file name for translated and compiled MO file must be the same as POT file with the addition of language code: {plugin-name}-{language-code}.mo.

You can check out this for translating plugins using POEdit program:
support.dev4press.com/kb/article/translating-plugins-or-themes-using-poedit

Does GD Security Toolbox Pro plugin works with WordPress MultiSite installations?

Yes. Plugin must be activated as Network Wide.