Capitalization (Headline style):
Turabian 17.1.2, p. 167: Capitalize most titles and subtitles headline style;
that is, capitalize the first letter and last words of the title and subtitle and all major words.
The subtitle, following a colon, is capitalized the same way as the main title:
Turabian 17.1.2, p. 168: For foreign-language titles, use sentence-style capitalization; that is
capitalize only the first letter of the first word of the title and subtitle and any proper nouns and proper adjectives thereafter.