Final answer:
A Hispanic teenager speaking only English in public and foregoing Spanish is displaying language assimilation, which is the process of adopting the dominant language and potentially losing the heritage language.
Step-by-step explanation:
A Hispanic teenager in the US who refuses to speak Spanish outside the home and only speaks English in public is exhibiting language assimilation. Language assimilation occurs when a speaker starts to prefer and primarily use the language of the dominant or mainstream culture, in this case English, while potentially losing proficiency in or ceasing to use their heritage language, which would be Spanish.
This process is common among immigrants and their descendants as they seek to fit into the dominant social and cultural norms of their new country.