Multilingual input field names switch back to main language

I am developing a multilingual wix website in three languages. On one of the pages, there is a custom form with many input fields and buttons. Some (but not all) of these elements behave strangely in terms of language: I translate the field names and button texts into the two extra languages and save my website; everything seems fine; when I return some time later, however, the field names and button texts have switched back to the main language of the site. It’s always the same elements that behave this way, although there seems to be nothing that distinguishes them from the other input elements and buttons.
Can anyone help to stop that unwanted behaviour?
Thank you very much.