Change / tweak existing wordpress translations

Question

I have a WP that has a custom theme, and all the translations working fine. Now I (i.e. my client) would like to tweak some wordpress-provided translations that live in /wp-content/languages/some_LANG.po.

Can I simply alter these files without fear of them being overwritten during an update, or should I handle this from my theme somehow?

For example I'd like to change (a bit) the messages related to password protected posts in the frontend.

Answer 1

It is better to use a separate file to prevent an overwriting during an upgrade.

Filter load_textdomain_mofile and replace the old file with your own:

add_filter( 'load_textdomain_mofile', function( $mofile, $domain )
{
    if ( 'name_of_the_textdomain' === $domain )
        return 'path_to_your_file.mo';

    return $mofile;
});