By default, each user will have their Work portal displayed in the Default language defined at the Global Culture setting of the project.
When having multi-language support and after having enabled additional languages as described at Multi-language support, each end user will be able to choose the language of their choice.
To choose a particular language, log in to Bizagi with your personal account and then go click on the Preferences menu option.
Select your preference from the Language drop-down list and click Update.
Recall that only the enabled languages are listed.
You may need to refresh your browser in order to view changes.