[ticket/13209] Fix expected request value of CPF language fields.

Multiple languages can be edited, thus the expected value is an array.

PHPBB3-13209
[ticket/13209] Gather language field values for boolean CPF's in all steps.

The user can move back and forth between all three steps and as such the lang
field data should be expected in all steps.

PHPBB3-13209
Merge pull request #3137 from prototech/ticket/13209

[ticket/13209] Fix loss of CPF language field values when switching steps