change spell checking language in Sharepoint Online

[WOLFITUS]

I want to select a different language in the spelling and grammar editor of Sharepoint Online. Where I can change it?

[#2]

The only place where you can change language and regional settings for given site is in the site settings page

[#3]

@WOLFITUS Unfortunately, in the SharePoint version of the Microsoft Editor it is SharePoint that chooses your language.  It is mostly the base language of the site that determines what language it thinks it is, and user settings don't change it.  You can install the browser extension version of Microsoft Editor to override it, and it gives you better language selection.  Here is a blog post about Microsoft Editor's language issues.
https://blog.icefire.ca/blogs/post/sharepoint-microsoft-editor-how-to-overcome-language-issues