ReCaptchaNoCaptcha API provides hl parametre to set user language (see https://developers.google.com/recaptcha/docs/display). Please use it and set to wiki user's language.
The hl attribute should be set in the script load tag of the api.js recaptcha widget code. You can get the language, the page is currently viewed in, using the RequestContext object, which handles all possible ways to change the display language automatically, using [[ https://doc.wikimedia.org/mediawiki-core/master/php/classRequestContext.html#aea752ea8e3670aca0a7e8550551cbf23 | getLanguage ]].