Current latest version of Gmail REST API Addon addon requires GD Mail Queue Pro version 5.0 or newer.

Gmail REST API Addon addon requires one of the following PHP versions: 7.0, 7.1, 7.2, 7.3, 7.4. The plugin might work with older PHP versions, but they are no longer tested or supported.

Gmail REST API Addon addon requires one of the following WordPress versions: 4.9, 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.

Gmail REST API Addon addon requires one of the following ClassicPress versions: 1.0, 1.1, 1.2.

Gmail REST API Addon addon is 1 year, 6 months old.

Gmail REST API Addon addon was first released on June 30, 2019.

Gmail REST API Addon addon latest version 1.2 was released on July 28, 2020.

The detailed changelog for Gmail REST API Addon addon is available here: Gmail REST API Addon Changelog.

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

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

No.

The addons are made for the GD Mail Queue Pro, and there are no plans to have addons supported in Lite/Free version.