Various solutions to this. One is to call insert_lang in API functions with the submitter user parameter of the function. Another is to fix it up after the API call finishes, resetting it to the correct Comcode owner for the import. Another one is a mass fix afterwards, with queries like:
UPDATE cms_translate t JOIN cms_f_posts p ON p.p_post=t.id SET t.source_user=p.p_poster,text_parsed='' WHERE t.source_user<>p.p_poster;
These approaches are not necessarily mutually-exclusive.