PHP function for swapping languages when changing the default language in ProcessWire

swap-languages.php

<?php

function swapLanguages($pages, $lang) {

	$startTime = microtime(true);
	$langDefault = "default";
	$log = ["languages" => "Swap field values for language {$langDefault} with {$lang}", "pages" =>[]];
	$languages = wire("languages");
	// get languages
	$l1 = $languages->get($langDefault);
	$l2 = $languages->get($lang);

	foreach ($pages as $p) {

		$log["pages"][$p->id] = "";
		$fieldlog = " name";

		$p->of(false);

		// swap page names
		$nameDefault = $p->localName($l1);
		$name = $p->localName($l2);

		if($nameDefault != $name && !empty($name)) {
			$p->set("name",$name);
			$p->set("status$l2",1);
			$p->set("name$l2",$nameDefault);
		} elseif($nameDefault != $name && empty($name)) {
			$p->set("status$l2",1);
			$p->set("name$l2",$nameDefault);
		}
		// iterate through all fields and swap multi language field values
		foreach ($p->template->fieldgroup as $field) {

			if($field->type instanceof FieldtypePageTitleLanguage || $field->type instanceof FieldtypeTextareaLanguage || $field->type instanceof TextLanguage) {
				$fieldlog .= " {$field->name}";
				// var_dump($p->$field); // needed this for some pages otherwise they threw an error
				// $p->of(false); // needed this for some pages otherwise they threw an error
				$langDefault = $p->$field->getLanguageValue($l1);
				$lang = $p->$field->getLanguageValue($l2);

				if( $langDefault != $lang && !empty($lang) && !empty($langDefault) ) {
					$p->$field->setLanguageValue($l1, $lang);
					$p->$field->setLanguageValue($l2, $langDefault);
				} elseif( $langDefault != $lang && empty($lang) ) {
					$p->$field->setLanguageValue($l2, $langDefault);
				} elseif( $langDefault != $lang && empty($langDefault) ) { // only needed this for pages that got created through API and had no default lang value set
					$p->$field->setLanguageValue($l1, $lang);
				}
			}
		}
		
		try {
			$p->save();
			$log["pages"][$p->id] = "Swapped values in fields: {$fieldlog}";
		} catch (Exception $e) {
			$log["pages"][$p->id] =  'Error: ' .  $e->getMessage();
		}

		$p->of(true);
	}

	// write logfile
	$logfile = fopen(wire("config")->paths->logs . "swaplanguage-log.txt", "w") or die("Unable to open file!");

	$iterator = new RecursiveIteratorIterator(new RecursiveArrayIterator($log));
	foreach($iterator as $key => $value) {
		fwrite($logfile, "$key => $value\n");
	}

	fclose($logfile);

	$time_elapsed = microtime(true) - $startTime;

	echo "Finished after {$time_elapsed} seconds";

}

/* Usage:
// swapLanguages($pages->find("template=basic-page, parent=1, include=all"), "de");
// argument 1: pages array
// argument 2: language name that you want to swap with the default language
// A log file will be written to site/assets/logs/swaplanguage-log.txt.
// It contains page IDs and fields that were swapped for each page
*/

/*
// After executing this function for all required pages, following steps are needed:
// 1. load core translation files for the language that is now your default (e.g. german translation files) to Setup->languages->default
// 2. change titles of the default Language to your language (e.g. Deutsch) and the language that got swapped (e.g. English)
// 3. if default language was English before swapping: delete core translation files for the language that you swapped
// 4. if default language was not English before swapping: load the core translation files for that language
// 4. in settings for home page, change the URL for your default language and the language that you have swapped.
// Example: 
// Before swapping: default was en, swap language was de 
// After swapping: default is now de, swapped language is now en
*/