About updating and localisation

Data: WP MU, 3.9.2

Recently I discovered that my custom Akismet's localisation was replaced by default one - 2 questions about auto updates and languages:

1) Does WP updates smth in wp-content/languages folder when auto updates?
I would like to keep all my custom localizstions (of all the themes and plugins I use) in this folder but now I am afraid that after WP auto update every custom localisation just disappear or will be replaced by default. Should I be worried about this or WP does not effect these?

2) What can I do to keep Akismet's custom localisation in safe from the plugin or WP auto update? OR: How do Akismet update it's default localisation and where Akismet stores it?

Regards.