444 would not stop a file being deleted. Deletion observes the permissions of the containing directory only. Whether the file is writable is irrelevant, because you’re not writing to it.
Other people have posted they results using the filter approach. I suggest you have a look through their follow ups.
Please note that 1.x version of this plugin is being phased out. If you have any issues please consider beta testing version 2.
The new version allows you to save files under wp-content/languages/loco/ – thus avoiding auto update overwrites. You can also configure the new version to use custom folders, such as woocommerce’s wp-content/languages/woocommerce/ path