Fix theme translations

fix-theme-translations.php

<?php
/*
Plugin Name: Fix theme translations
Description: Try to fix missing theme translations.
Author: Seebz
Author URI: http://seebz.net/
Version: 1.0
*/

function load_textdomain_mofile_fix( $mofile ) {
	// Cached value of `/path/to/wordpress/wp-content/themes`
	static $theme_root = null;
	if ( is_null( $theme_root ) ) {
		$theme_root = get_theme_root();
	}

	// Valid (existing) `$mofile`
	if ( file_exists($mofile) ) {
		return $mofile;
	}
	// Not-a-theme `$mofile`
	if ( strpos( $mofile, $theme_root ) !== 0 ) {
		return $mofile;
	}

	// Maybe the new (mo)file path
	$mofile = ftt_locate_mofile( $mofile );

	return $mofile;
}
add_filter( 'load_textdomain_mofile', 'load_textdomain_mofile_fix' );


/**
 * Lookup for an alternate mofile.
 * 
 * @param string  $mofile  Original (missing) (mo)file path
 * @return string Path of the new (found) (mo)file or original path if none found.
 */
function ftt_locate_mofile( $mofile ) {
	$basename = basename( $mofile );      // fr_FR.mo
	$locale = basename( $mofile, '.mo' ); // fr_FR

	// Possible paths
	$t = strtolower( $locale ); // fr_fr
	$paths[] = str_replace( $basename, "{$t}.mo", $mofile );

	$t = str_replace( '_', '-', $locale ); // fr-FR
	$paths[] = str_replace( $basename, "{$t}.mo", $mofile );

	$t = strtolower( $t ); // fr-fr
	$paths[] = str_replace( $basename, "{$t}.mo", $mofile );

	$t = preg_replace( '`[-_].+$`' , '', $locale ); // fr
	$paths[] = str_replace( $basename, "{$t}.mo", $mofile );

	// Loop over each path
	foreach( $paths as $path ) {
		if ( file_exists( $path ) ) {
			return $path;
		}
	}

	return $mofile; // Fallback to default
}