The language of the Payment Page is basically defined by the browser, but can be changed here with wallee in the Resources > Editor: under: Resources/web/template/form/element/ payment-card-data (folder)
All Twig files available here are responsible for a part of the translation.
Here words can be adapted or translations can be done.
card-holder.twig contains the word "card holder name".
By saving and publishing in the corresponding language, the display will be adjusted and shown accordingly.