Joachim Raff's Op. 114 '12 Zweistimmige Gesänge' (Two-Part Songs) are likely composed with intricate two-part counterpoint, demanding clarity and independence of lines. These pieces would showcase Raff's skillful contrapuntal writing within a Romantic harmonic framework.
The primary technical focus is on achieving perfect independence and clarity between the two melodic lines.
12 Zweistimmige Gesänge (Op.114) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
12 Zweistimmige Gesänge (Op.114) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.