"Lang, lang ist's her" is a little unusual, for a German song that is, as it is supposed to be a translation of an 18th century Irish folksong, "Tell me the tales". I've not yet come across the original song. The version I sing can be found in Lieder, Songs und Gospels 3.
This is a sad little song, just two verses, of a lovers' separation which happened a long, long time ago.

Lyrics