Definition
inner adj 1. (located in the interior) interno, -a, interior; in the ~ London area en la zona céntrica de Londres 2. (deep) íntimo, -a; (secret) secreto, -a; one's ~ feelings los sentimientos más íntimos de uno
(from Diccionario Cambridge Klett Compact)
Definition
interior I adj 1. (inner, inside, internal) interno, -a; (light) interior; the ~ market el mercado interior 2. (central, inland, remote) del interior II 1. (inside) interior m; the ~ of the country el interior del país 2. POL (home affairs) the Ministry of the Interior el Ministerio de Interior; the U.S. Interior Department el departamento de Interior de los Estados Unidos
(from Diccionario Cambridge Klett Compact)
Hmmm ... my conclusion is that when you are referring to "tangible" things, thins you can touch and see you have to use "interior" and if you are talking about things you can't see or touch liske feelings, etc... you must use "inner".
Let's see what the experts tell us.
Please correct me