Overwrite textdomain of plugins by default – Lost Translation

WordPress is awesome, but there is something that is driving me crazy.

Whenever a plugin or a theme is updated, all files are deleted and replaced.
So if I have custom code or a translation in one plugin, it will get lost!

I’ve seen some solutions suggesting to change the textdomain of the plugin to load language files from wp-content/languages, but if I write a custom function to load the *.po and *.mo from wp-content, directly in the plugin code, it will get overwritten too.

So I was wondering how I can update my plugins, without losing the translation or the custom code.

I ended up with WPML strings that do the job, by saving translation in DB, ( I’m not sure if is the way) but WPML is a very heavy plugin, and I will have to install it in all sites, which makes it difficult to maintain.

Is there any function to overwrite all textdomains of a plugin, so I can have all of the translations in wp-content/languages, without changing plugin code?