Not just language

When a writer takes a poetic form from another language without using words from that language, can the text be considered multilingual?  Not strictly, of course, because the other language apparently is absent from the text.  But if we take the broader view of linguistic mixing as not just appropriating words but also ideas and cultures, then yes.  A poetic form in a language arises from the distinctiveness of that language.  When a form is adopted or even adapted by a writer writing in another language, some of that "foreign" culture must necessarily also travel across languages and cultures to the writer's text.

Here is a description of what happens in Jarcha:

"One very distinctive form of the Hebrew poetry is the Jarcha. This poetic style is an example of the development of Arabic poetry, mixed with Jewish themes, to create a new poetry. The Jarcha is a lyrical poem that repeats the final verses of an Arabic structure. Yosef the writer's Jarcha, dated 1042, is considered not only the oldest text of Romance Spanish, (The Poema de Mio Cid is dated 1140), but the oldest lyrical text of any European Romance language. Consequently it becomes evident that Sephardic poetry is very important for all of Romance literature, as well as for its own culture. Below is a translated quartet from a Jarcha, which tells the Biblical story of Joseph:

'Joseph always feared the mighty Lord of Hosts
And was with his brothers a shepherd of the flocks.
At that time it was that he sinned one of the sins,
Causing them to quarrel with their father over Joseph.'

"Some poets wrote with a Muslim structure, while writing in Hebrew. Other poets, like Ibn Gabirol, wrote in many forms, with different rhymes and rhythms. The Sephardim remained faithful to their Biblical education and often used images and stanzas from the Torah. Much of their poetry was direct quotation from the Bible, which they adapted into original formats. You can see this format in the above example of the Poem of Joseph, which is a fine example of the mixing of Spanish and Jewish styles."

Writers from one country routinely borrow or adapt poetic forms from another country.  The effect of the other country's culture (not just the forms nor the language) on the literature of the receiving country is another open area for research among younger critics looking for a dissertation topic.