It should not affect rankings. Technically, traffic should improve by having multiple locales.

With our sites at (https://pinkpigeon.co.uk), we use sub-directories, such as example.com/fr.

This guy has some good info (but is a bit spammy with the hard sell): https://neilpatel.com/blog/international-seo/

And here is some more info I have found useful in the past: https://translatepress.com/seo-multiple-languages/