I have installed Cookies Policy plugin.
How can I make message available in Spanish rather than in English, or, how plugin decides which language shall be used? (there is language.yaml with several languages).
Thanks
In the file you cite (language.yaml) you have to add strings for spanish (and, of course, have the langswitcher plugin running and the default language for Spanish).
After adding Spanish you could propose a PR to the plugin author at this address https://github.com/giansi/grav-plugin-cookies-policy/pulls