Unfortunately, you can't change the language of the entire app, but before creating a board you can choose an existing template, according to your language.
We have existing templates in English, Portuguese, Spanish, French, and German.
In case you don't find existing templates in your language, you can customize the columns of your board to any language you want.
Here’s an example of creating a customized board in Portuguese:
Note: If you want, you can suggest a new template in your language. To do that click on the "Suggest a new template" option.