This appeared on the German translation mailing list.

It's just plain wrong.

"Sentence case: The most common in English prose. Generally equivalent to the baseline universal standard of formal English orthography mentioned above; that is, only the first word is capitalized, except for proper nouns and other words which are generally capitalized by a more specific rule."

Please change the misleading word to a phrase that properly describes what the function does. How about "Only first letter capitalized"?