Complex sentence: A similar development can be found in the Anglo-Frisian languages Old Frisian and Old English, but in Old English the West Germanic "ai" became "ā" and "au" became an "ēa"-sound.
Split into simpler sentences: A similar development can be found in the Anglo-Frisian languages Old Frisian and Old English. In Old English the West Germanic "ai" became "ā" and "au" became an "ēa"-sound.