Add assets to a board

Specifies the board to add assets to.

Provide a header to specify the language of result values. Supported values: cs (iStock only), de, en-GB, en-US, es, fi (iStock only), fr, hu (iStock only), id (iStock only), it, ja, ko (creative assets only), nl, pl (creative assets only), pt-BR, pt-PT, ro (iStock only), ru (creative assets only), sv, th (iStock only), tr, uk (iStock only), vi (iStock only), zh-HK (creative assets only).