What technique is it when you use strings of another language in an English poem?

In Wilfred Owen's poem he ends with "Dulce et decorum est/Pro patria mori". I wonder if there is a recognised term to refer to this technique. Another example of its use is in T.S Eliot's "The Wasteland", where he has lines in German and French such as "And drank coffee, and talked for an hour. Bin gar keine Russin..."

Solution 1:

Plurilingualism is switching between languages.

Heteroglossia is a more general term for the juxtaposition of different kinds or styles of speech and can refer to mixing high and low registers or dialects or languages. Bakhtin considered this a defining characteristic of some types of literature.

Solution 2:

Code switching is used to refer to this, even in poetry:

In linguistics, code-switching or language alternation occurs when a speaker alternates between two or more languages, or language varieties, in the context of a single conversation or situation. — Wikipedia

For example:

• Code-Switching in Bilingual Chicano Poetry
• Code-Switching in Poetry: “Crickets in Three Languages”
• The function and significance of bilingual code-switching in English poetry with a special focus on the work of Eliot and Pound