According to Wikipedia: “Ä occurs as an independent letter in Finnish, Swedish, Skolt Sami, Karelian, Estonian, Luxembourgish, North Frisian, Saterlandic, Emiliano-Romagnolo, Rotuman, Slovak, Tatar, Gagauz, German, and Turkmen”

Æ is, according to Wikipedia, used in Latin, Icelandic, Danish, Norwegian, Faroese, Ossetic, Kawésqar, and Yaghan. (It is not used in French or English except in loanwords from Latin.)