A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Special terms - Foreign language terms
Names, special terms, and titles of works
Part III. Style 20 spelling

Some special terms require use of italics, quotation marks, and capitalization.

22.2.1 Foreign language terms

Italicize isolated words and phrases in foreign languages likely to be unfamiliar to readers of English, and capitalize them as in their language. (If you are unfamiliar with the capitalization principles of a language, consult a reliable authority such as chapter 10 of the Chicago Manual of Style, 15th edition [2003].) For titles of works in foreign languages, see 22.3.1.

This leads to the idea of bermensch and to the theory of the acte gratuit and surrealism.

Do not italicize foreign terms familiar enough to appear in Merriam-Webster's Collegiate Dictionary.

de facto

vis-à-vis

pasha

eros

Do not italicize foreign names or personal titles that accompany them.

Padre Pio

the Académie Française

the Puerto del Sol

If you define a foreign term, put the definition in parentheses or quotation marks, either following the term in the text or in a note.

The usual phrase was ena tuainu-iai, “I wanted to eat.”

According to Sartrean ontology, man is always de trop (in excess).

For longer quotations from a foreign language, use roman type. Italicize the quotation as a whole or any words within it only if they are italicized in the original. Enclose the quotation in quotation marks within the text or use a block quotation following the principles in 25.2.

The confusion of le pragmatisme is traced to the supposed failure to distinguish “les propriétés de la valeur en général” from the incidental.