The commands that should be added to /etc/bash_profile to change the language of messages from an internationalised program to Portuguese (pt) are:
export LANG="pt"
export LC_MESSAGES="pt"
The LANG and LC_MESSAGES environment variables are used to control the language of messages from an internationalised program. The LANG variable sets the default locale for all categories, such as collation, currency, date and time formats, etc. The LC_MESSAGES variable sets the locale for the language of messages, overriding the LANG variable for this category. Therefore, to change the language of messages to Portuguese, both variables should be set to "pt" in /etc/bash_profile, which is a script that is executed when a user logs in. This will affect the current user and any subsequent login sessions.
Reference:
Locale Environment Variables in Linux - Baeldung on Linux
Environment Variables - The Open Group
[LPI Linux Essentials - 1.4 Localization and Internationalization]