May the terms defined in the RAL such as “feathers which have not previously been used“, “half-down“ and so on still be used?

No, they must not. The regulations of the RAL 092 A2, which was in force in Germany between 1932 and 2004, and which provided the definition of these terms, was repealed with effect from December, 31^st 2004. The suppliers of bedding are not allowed use these regulations anymore since January 1^st 2005, neither for labelling nor for purposes of advertising.