I have a guess how one can erroneously think that 'lokkigten' is an old dialect version.

In modern German it is 'lockigen' and in old German it was the same, or 'lockigten' but never 'lokkigten'. However, in old songbooks, the lyrics to the first verse were usually printed below the notes of the tune. In these cases, the words were printed separatedly into syllables when the syllables were sung to different notes in order to show how the tune was thought to fit the lyrics.

If 'lockig' is separated into syllables it is 'lok-kig' (in the German before the recent revision). That's how this word is printed in my quite old Christmas songbook. So the original lyrics may have been 'holder Knabe im lockigten Haar' appearing in the print below the tune as 'hol-der Kna-be im lok-kig-ten Haar'.

(I can't read the reprint in Q's link, as hard as I try)

Wolfgang