'[Rahmencurriculum]1' (Ger.) translates to model curriculum (curriculum according to a specific framework) in English. The reference is to curriculum.
It is clearly not curricular framework in OP's case.
[EDIT]
A framework curriculum is a sample/ model built on the basis of guidelines (the 'framework'). Individual institutions can design their curricula on this model, or probably adopt it as such.
A curricular framework (loosely, curriculum framework) is a set of guidelines defining and explaining what a curriculum is required to be like or contain.
The basic difference between the two is emotions it appeals to.
Fun is enjoyable. It causes pleasure - especially in active forms, as thrill, exhilaration, challenge, elation.
Interesting appeals to curiosity - learning, it's about things we want to know, see, learn, examine. Whatever reasons - be it for pleasure, or e.g. for professional interest or satisfying anxiety.
Since usually satisfying curiosity is pleasurable, these two are often correlated, but not always. A gruesome sight, say, bowels sticking out of a live person's ruptured abdomen, may be interesting, but definitely not fun. A secret document on enemy military movements will be interesting too, but definitely not fun. The pilot of a damaged airplane will definitely find the damage report interesting and absolutely not fun.
On the other hand, if you solved a hundred crosswords, solving one more may still be fun, but hardly interesting. Riding down a slide in entertainment park will be described as fun too - it may be interesting the first time, but then you're not curious about it any more, you just do it for fun. Being given unexpected presents is fun - but since you didn't expect them, you didn't have time to find that interesting.
Best Answer
In "a size bigger", "size" is used as a unit of measurement.
This usage presumes that whatever is being discussed (clothing, drink servings, etc.) comes in a discrete set of possible sizes. Thus, for example, if a café serves coffee in "small", "medium", "large" and "extra-large" cups, then a medium coffee would be "a size bigger" than a small coffee (and a large coffee would be two sizes bigger than a small, and an extra-large would be three sizes bigger than a small).
Compare this with other similar unit-based comparisons, like "He's an inch taller than her" or "This road is a mile longer than the other one" or "This ladder is two steps taller than that one."
On the other hand, "a bigger size" simply refers to any size that is bigger than the one it's compared to. So, in the same café example as above, "medium", "large" and "extra-large" would all be bigger sizes than "small".