Export/Import a translatable csv in ProcessWire

_init.php

<?php

include_once "path/to/import.php";
include_once "path/to/export.php";

// call the functions like this
if (isset($_GET["export"])) {
	$forceDownload = isset($_GET["force"]);
	$debug = isset($_GET["debug"]);
	renderExport($pages, $forceDownload, $debug);
} else if (isset($_GET["import"])) {
	import();
}

export.php

<?php 

function renderExport($pages, $force, $debug) {
	// allowed fields
	$allowedFields = array('title', 'headline', 'summary', 'body', 'body_secondary', 'text', 'image', 'images');

	// get current user
	$user = wire('user');

	// get all installed languages
	$languages = wire('languages');

	// first line of generated csv
	// add url so translator has some context
	$headLine = array("fieldID");

	// a single page = one line in csv
	$page = array();

	// field data export
	$export = array();

	// find all pages
  // exclude configuration pages
	$selector = array("has_parent=1", "include=all", "include=hidden", "has_parent!=3|22|21|28|304|23|1035|1142|1447|/trash", "id!=3|22|21|28|304|23");
  
	// pass some variables per reference so that they can be used later for output
	$pages->findMany(implode(",", $selector))->explode(function ($resultPage) use (&$export, $page, &$headLine, $languages, $allowedFields, &$user, $debug) {
		$resultPage->setOutputFormatting(false);
		// loop through allowed fields
		foreach ($allowedFields as $field) {
			// check if field exists on page
			if ($resultPage->hasField($field)) {
				$getField = $resultPage->get($field);
				// special snowflake: RepeaterMatrix is just an array of pages
				if ($field === "image" | $field === "images") {
					$fieldIdentifier = $resultPage->id . "#" . $field;
					// remember user's language
					$lang = $user->language;
					$i = 0;
					foreach ($getField as $image) {
						$imageIdentifier = $fieldIdentifier . "#" . $i;
						$i++;
						$translatedValues = array();
						// loop through languages
						foreach ($languages as $language) {
							if (!in_array($language->name, $headLine)) {
								array_push($headLine, $language->name);
							}
							$user->language = $language;
							if ($image != null) array_push($translatedValues, $image->description);
						}
						// restore saved language
						$user->language = $lang;
						$page = array($imageIdentifier, preg_replace("/\r|\n/", "", implode(";", $translatedValues)));
						array_push($export, $page);
					}
				} else {
					$fieldIdentifier = $resultPage->id . "#" . $field;
					$translatedValues = array();
					// loop through languages
					foreach ($languages as $language) {
						if (!in_array($language->name, $headLine)) {
							array_push($headLine, $language->name);
						}
						if ($resultPage[$field] !== "") {
							array_push($translatedValues, str_replace('"', '&quot;', $resultPage->get($field)->getLanguageValue($language->id)));
						}
					}
					$page = array($fieldIdentifier, preg_replace("/\r|\n/", "", implode(";", $translatedValues)));
					array_push($export, $page);
				}
			}

		}
	});
	array_unshift($export, $headLine);
	renderExportCSV($export, $force);
}

function renderExportCSV($export, $force) {
	// force download as file and set correct headers
	if ($force) {
		header("Content-type: text/csv; charset=utf-8");
		header("Content-Disposition: attachment; filename=" . $_SERVER['HTTP_HOST'] . "-" . date("Ymd") . ".csv");
		header("Pragma: no-cache");
		header("Expires: 0");
	}
	$output = "";
	// generate CSV syntax
	foreach ($export as $exportItem) {
		$output .= '"' . implode('";"', $exportItem) . "\";\n";
	}
	echo $output;
	exit();
}

import.php

<?php 
function import() {
	$pages = wirePages();
	$csv = csv_to_array(wire('config')->paths->templates . 'lib/csv.csv', ';');
	$languages = $csv[0];
	// remove id and url from languages
	#unset($languages[1]);
	unset($languages[0]);
	unset($csv[0]);
	var_dump($languages);

	// loop through rows of csv
	foreach ($csv as $item) {
		#var_dump($item);
		// { 23, title }
		$fieldIdentifier = explode("#", $item[0]);
		$p = $pages->findOne("id=$fieldIdentifier[0], include=all");
		// if page exists
		if (!$p instanceof NullPage) {
			#var_dump($p->title);
			// turn off output formatting
			$p->of(false);
			$i = 0;
			$user = wire('user');
			foreach ($languages as $lang) {
				$user->language = wire('languages')->get($lang);
				$i++;
				var_dump($item[$i]);
				if (!empty($item[$i])) {

					if ($lang === "") continue;
					if ($fieldIdentifier[1] === "image" | $fieldIdentifier[1] === "images") {
						if ($fieldIdentifier[1] === "images") {
							$images = $p->get($fieldIdentifier[1]);
							$image = $images->eq($fieldIdentifier[2]);
						} else {
							$image = $p->get($fieldIdentifier[1]);
						}
						$image->description = $item[$i];
						//var_dump($image);
						var_dump("Set " . $item[0] . " to " . $p->get($fieldIdentifier[1] . "_" . $lang) . " for Lang " . $lang);
						continue;
					}
					$string = str_replace('&quot;', '"', $item[$i]);
					var_dump($string);
					$p->set($fieldIdentifier[1], $string);
				}
			}
			$p->save();
		}
	}
	exit();
}

function csv_to_array($filename = '', $delimiter = ',') {
	if (!file_exists($filename) || !is_readable($filename)) return FALSE;

	$data = array();
	if (($handle = fopen($filename, 'r')) !== FALSE) {
		while (($row = fgetcsv($handle, 10000, $delimiter)) !== FALSE) {
			array_push($data, $row);
		}
		fclose($handle);
	}
	return $data;
}

The output will look like this:

"fieldID";"default";"english";"russian";"chinese";
"1#title";"Default Title";"English Title";"Russian Title"; "Chinese Title"

and can be given to a company offering translation services.
The import file should look the same, the fieldID field has to stay the same all the time.

Backup the database BEFORE doing any imports