I checked a few books on Saints, and they agreed on the fact that his life is not reliable. Some suspect that he was of Frankish origin rather than Irish.
"His unreliable Life discribed him as an Irishman who ..." (D.Farmer, The Oxford Dictionary of Saints, 1997)
"The uncertain life, covered by legends, says Fridolin was of Irish, but rather of Frankish descent" (Schauber & Schindler, Bildlexikon der Heiligen, München 1999)
"... probably of Frankish descent ..." (
Clemens Jöckle, Das Große Heiligenlexikon, Köln 2003
"His Germanic name is a point against his Irish descent." (Lexikon der Heiligen und Heiligenverehrung, Freiburg 2003)
FRIDOLIN is a typical southern
German name, by the way, at home in Swabia. And indeed -lein / -lin is the diminutive used in the south of Germany (and -chen / -ke(n) rather in the north).