Salam Reza,
1.
Change the default locale
XXX - Needs updating
By default, the BigBlueButton client should detect the browser’s locale and use that default language accordingly.
The default language is English, but you can change that by editing bigbluebutton/client/BigBlueButton.html and change the value
localeChain = "en_US";
2.
I recommend also to search the file /usr/share/meteor/bundle/programs/server/assets/app/config/settings.yml for „locale“ .
There are some settings related to locale:
fallbackLocale: en
overrideLocale: null
localesUrl: /locales
3.
Any Greenlight‘ system-user can use profile to set preferred locale. Also Greeenlight Adminsitraor can set the locale for system-users.
I hope, this helps you.
Asghar