Currently, Grammarly supports only the English language.
With that being said, Grammarly recognizes a number of spelling, grammar, and punctuation differences in American, British, Canadian, and Australian English.
You can change your language preference at https://account.grammarly.com/customize
You can also set up your language preference in the Grammarly extension: simply click the Grammarly icon in your browser's toolbar and select your preferred setting in the dropdown menu next to I write in.
To learn more about the Language preference feature, please visit this page.