Writing to "Option" Fields


Has anybody successfully written to collection fields that are “dropdowns”? I’ve got one field, language, with just two choices, and no matter what I try to POST to the database, I keep getting validation errors like:

"Field 'language': Value is not an allowed Option: 'English'"

In the docs here on the “options” field, it says that it’s expecting an array; while right above it, it says the Option field is a string. I’ve tried both! And for the life of me I can’t get it to POST. Any ideas? Everything else works fine… if I make the field not required, I can POST data without it. But that’s not really a solution!