WPML

I'm not sure what you mean?

my theme GENERATEPRESS is compatible with WPML ?
I would understand if I have to use the WPML’s String Translation.

I can't use WMPL. I bought GP because the details were specified compatibility with WMPL and Translation & RTL Ready.
But I wrong. I am very distressed.

Thanks

WPML should work with GP right away. Here's confirmation: https://generatepress.com/forums/topic/multilanguage/

Are you running into any specific issues?

Ok! Perfect!
I can't translate. Anything.
I think I do something wrong in the section Theme and Plugins Localization.

Sorry.

No problem! Glad it's working :)

What should I choose?

"WPML allows to create translations for texts in themes and plugins in two ways: Don’t use String Translation to translate the theme and plugins (translating using the traditional .mo files). It’s good when you already have a theme with the translations you need.

Translating theme and plugin texts using WPML’s String Translation."

Thanks

I haven't personally used the plugin, so I'm not sure.

Give each of them a try and see which works best for you :)