[WIP][BUGFIX] Language overlay for displayCond / subtype

Before a displayCond field value or the subtype_value_field value is
used a language overlay is performed to make sure that the l10n_mode
configuration is taken into account.

WIP: language overlay for subtypes.

Resolves: #59130
Releases: 6.2
Change-Id: I0fdcdcb86e6201f454f8b6ede3ee519f53da8ff1