+0
Hi,

North (adj) and northern (adj) are interchangeable? If not, how can we distinguish them clearly?

Ex: North London = Northern London? (1)

The north bank of the river. =The northern bank of the river? (2)

The north slopes of the mountains. =The northern slopes of the mountains. ?(3)

North Scotland. = Northern Scotland? (4)

North accent =Northern accent? (5)

North climate = Northern climate? (6)

Quoc
Comments 
I'm sorry but there isn't an easy way to look at this.

Some are interchangeable (north/northern bank of the river).

Some are not (northern accent, northern climate).
This has always been a difficult one for me to explain too. Nona points out that "accent" and "climate" can't be used with "north". I'd say that's because "north" indicates a well-defined physical position. However, where there is such a definition they seem to be interchangeable. Some names are established by tradition, so we usually say North London (the part north of the Thames), but Northern Ireland (the part north of the border).
Not much help, I'm afraid.
Tung Quoc:

All the page is full up with your questions like that... English is not mathematics, it is just a language..

You don't need to question the grammar of the language like that because I believe that there is no formula or explanation for the most of your questions....

cheers...
Tung QuocHi,

North (adj) and northern (adj) are interchangeable? If not, how can we distinguish them clearly?

Ex: North London = Northern London? (1)

The north bank of the river. =The northern bank of the river? (2)

The north slopes of the mountains. =The northern slopes of the mountains. ?(3)

North Scotland. = Northern Scotland? (4)

North accent =Northern accent? (5)

North climate = Northern climate? (6)

Quoc
You can add northerly winds to the lot.

Cheers
CB