Create multivariables inputs in vendor registration form

-- HikaShop version -- : 2.6.0
-- HikaMarket version -- : 1.6.7

Hello,
i would like to create complex inputs for a vendor . For example (see image sent):
- have the possibility to add as many languages spoken by the vendor (with for each language added, a dropdown list with options coming from a database table of my own)
- give a mastery score for a list of "sectors" for the vendor (with for each competence, several radio buttons, all coming from a database table of my own)
For both of them i was able to build a complete form, loading the values, saving,....(using a $jinput function).. When I save the results, I "implode" some values (languages is a simple implode, so my database "languages" field becomes "id_language1,id_language2,..."; for the "sectors" i built a more complex way with the id of the competence and its score separated by a ::, so I have my database "sectors" field as "id_sector1::score1,id_sector2::score2,...")
I would like to integrate this type of fields/form in the vendor registration but I am stuck.
I started to do the following :
- I created vendor custom fields (languages, sectors,...)
- I edited the "registration.php" view; for each of my add custom filed, I was able to show the fields exactly as in my own form,...

but I don't know how to collect the answers, "implode them" and save them when using the Hikamarket registration form. The key problem is that because of these necessary "implodes", I need to collect the values and "implode" them before they are collected by the Hikamarket function getting the fields and saving them (which is/are the functions that I don't know of)

Could you tell me the how to do it?