This canvaswork stitch is a variation on mosaic stitch.  Both are worked diagonally over one or two intersections of canvas: condensed mosaic stitch forms diagonal lines whereas mosaic stitch forms small squares.

This stitch dates from at least the 19th century, as it appears in an 1842 publication from the USA (The handbook of needlework) under the name ‘German stitch’.  Later in the same century ‘German stitch’ is also listed as one of the stitches used in Berlin woolwork.