‘few’ and ‘a few’ both mean not many and the decision whether to use ‘few’ or ‘a few’ may largely depend on the rules of grammar.
‘few’ emphasizesnot many and is not infequently used with very. There are (very) few people who can speak 12languages.
‘a few’ can also emphasize not many and is often used with only or just. There are (only) (just) a few people who can speak 12 languages.
On the other hand ‘a few’ can emphasize that there actually are some of whatever you are talking about. Therefore ‘a few’ is used in the positive sense. Thereactually are a few people who can speak twelve languages. Won’t that take afew lifetimes?