I have tried:

• Poedit (from my computer);
• Codestyling Localization (appears broken);
• MyWPTranslate (which normally always works).

I would love to translate the comment-form.

This is very short description so not sure whether you have followed all the instructions.

Please follow all the instructions as described on the following page to translate the theme.

https://colorlib.com/wp/how-to-translate-wordpress-theme/

And please also, I have tried 3 different cache (Comet Cache, WP Fastest Cache and WP Super Cache) plugins, but they do not seem to make my site any real faster.
Which one would you recommend? And should I readjust my images so that my site will be blazing fast? As was promised before I purchased your theme.

We recommend the plugin https://wordpress.org/plugins/w3-total-cache/ but it is not sufficient to make your site load blazing fast. Along with this you have to also implement the various solutions shared on the following pages.

https://codex.wordpress.org/WordPress_Optimization

https://gtmetrix.com/wordpress-optimization-guide.html

https://techtage.com/speeding-up-wordpress-sites/

And can you please inform me why – everytime I make changes to the child’ style.css – both Firefox and Chrome are not showing changes. Only Safari does. Is your theme not compatible with Firefox and Chrome??

The theme is compatible with Firefox, Chrome and all other latest versions of browser. There are various reasons as following that can cause not to work your CSS code so please check it.

1 Your CSS code is only compatible with safari browser.

2 Clear your browser cache

3 Clear the cache from (Comet Cache, WP Fastest Cache and WP Super Cache) plugins that you are using on your site.