Recent problem: customer wanted his reCatpcha forced to german language. First attempt was to set the setting via the RecaptchaOption Script variable. Howewer, for some reason this did not work.
Here is the solution:
<script type="text/javascript"
src="http://api.recaptcha.net/challenge?k=apiKey<strong>&hl=de</strong>">
By adding &hl=de to the "src" URL the language was forced to german.