Translation of default wordpress registration

We have added additional fields to the default wordpress registration using the Profile Extra Field plugin. We want to translate for them. This plugin itself does not add String Translation to Polylang, so we installed Theme and plugin translation for Polylang (TTfP) plugin and scanned the Profile Extra Field plugin, but the field names did not appear in String Translation. We also tried to add String Translation ourselves using the pll_register_string function, but the call function could not be inserted into the field name, because after saving the php changes, the code is erased from the field name. How can we translate additional fields for default wordpress registration? Will the paid version of Polylang help us with this? If so, which paid version of Polylang is right for us?