The C128 was given a double-sized CHARROM which consists of the C128 characterset and the C64 characterset, both used in respective mode. The fonts differ in lowercase b, d, f, h, i, j, k, l, m, s, t, u, w and y (all C128 chars are equal to the plus/4 except for the m). Early C128 prototypes had only one font but there were some compatibility issues so they had to include the original font to be used in the C64 mode.

C64 characterset vs C128 characterset
 
National (SE/FI/DK/NO etc) models use the same font between C128 and C64 mode because the other bank is used to store the national characterset. You can switch between the charactersets using the CAPS LOCK-key. National models also have a 2764 ROM and a 2364 to 2764 adapter, you can see the differances in an earlier post C128 vs C128d motherboard. The upper picture is a US C128 and the lower picture shows a SE/FI C128. Depending on the region, the CAPSLOCK-key can have different printings; “CAPS LOCK”(US), “ASCII/DIN”(DE), “CAPS LOCK ASCII/CC”(SE/FI) and possibly some more.

If the CHARROM(U18) needs replacement, the pinout is a 2364(8K) ROM. You can replace it with a 2764 using 2364 to 2764 adapter (note that there is not much space under the RF-shield).

 
 

National modifications for C128

SE/FI machine. The brown wire connects jumper “J7” and CHARROM pin 21 together allowing CHARROM bankswitching using the CAPS LOCK key.
 


Closeups of the modifications. CHARROM lifted out of the socket to see where the bankswitching wire is connected. The trace near C19 is cut and the wire connected to the rightmost pad of J7.
 


C128 CHARROM. SE/FI characterset with a factory 2364-to-2764 adapter.
 
 

C128 Character ROM, U18, partnumbers
390059-01 US (2364)
315079-01 DE (2364)
315079-02 DE
325173-01 CH
325175-01 DK
325175-02 DK
325171-01 ES
325167-01 FR/BE/IT
325178-01 NO
325181-01 SE/FI