Updating the Recaptcha language from English to another language is possible by adding a small script at the header section of your form.
Recaptcha with updated language.
Here's how to add the script code to change reCaptcha language:
1.) Edit your form, go to "Form Settings > Edit Header/Footer"
2.) In the Header/Footer dialog box, select HTML, click on the "Source" button in Header, and paste in all of the code from the attached text (.txt) file below. Click the red "Close" button on the dialog box then SAVE your form.
And that's it! Your recaptcha language should now be changed.