fatal error in mo.php line 83

I get this error in (apparently) any page of my wp site. Googleing the error message returns other wp sites with the same problem.

Fatal error: Maximum execution time of 1200 seconds exceeded in .../wp-includes/pomo/mo.php on line 83

Here is the code block from mo.php:

function import_from_reader($reader) {
		$reader->setEndian('little');
		$endian = MO::get_byteorder($reader->readint32());
		if (false === $endian) {
			return false;
		}
		$reader->setEndian($endian);

		$revision = $reader->readint32();
		$total = $reader->readint32();
		// get addresses of array of lenghts and offsets for original string and translations
		$originals_lo_addr = $reader->readint32();
		$translations_lo_addr = $reader->readint32();

		$reader->seekto($originals_lo_addr);
		$originals_lo = $reader->readint32array($total * 2); // each of
		$reader->seekto($translations_lo_addr);
		$translations_lo = $reader->readint32array($total * 2);

		$length = create_function('$i', 'return $i * 2 + 1;');
		$offset = create_function('$i', 'return $i * 2 + 2;');

		for ($i = 0; $i < $total; ++$i) {
			$reader->seekto($originals_lo[$offset($i)]);
			$original = $reader->read($originals_lo[$length($i)]);
			$reader->seekto($translations_lo[$offset($i)]);
			$translation = $reader->read($translations_lo[$length($i)]);
			if ('' == $original) {
				$this->set_headers($this->make_headers($translation));
			} else {
				$this->add_entry($this->make_entry($original, $translation));
			}
		}
		return true;
	}

and this is the 83rd line:

$this->set_headers($this->make_headers($translation));