The MLA Style Center says, "In MLA style, titles of English-language works are capitalized headline-style, and titles of works in languages other than English are capitalized sentence-style. This distinction is somewhat arbitrary but accords with other usage guides."
and,
"The MLA Handbook also explains what to capitalize in titles and when to do so (1.2.1, 1.2.5). Partly, these distinctions are a matter of convention and are intended to respect the ways in which various languages have evolved. In titles capitalized sentence style, for instance, words are capitalized if they are capitalized in the foreign language. For example, in German all nouns are capitalized, but not all nouns are capitalized in French, so this difference is reflected in which words are capitalized in German and French titles.
Using headline style for English titles and sentence style for titles in languages other than English helps maintain consistency and provides a simple and concise guideline for styling titles."
