Import multiple options in one field
If you are using Multi-value Custom Data, see How to import to multi-record set custom fields and the answer.

But it sounds like you are importing multiple options in a field, in which case you can use comma separated values in a single cell. The import file will look something like this:

First Name,Last Name,Language
Joe,Smith,"English, Spanish"
Frank,Jones,"Dutch, English"


Tip: Try exporting a couple of existing records (with similar data) to see what CiviCRM expects in the import.