I'm struggling to replicate this error and see the cause. A number of our instructors are seeing "undefined" in the Grade Centre for a decimal point. This occurs when we apply a modified language pack.
We've noticed also that the date format changes from UK/GB to US.
We've been customising the language pack for several BB versions now and not see this before.
I download the current UK language pack for each version, modify it (change "module" to "widget" to avoid confusion) and then edit the manifest to provide a new name/locale e.g. en_GB_something. A screenshot is included below.
I can't see what's wrong with our language pack which causes the decimal (property?) to be lost and also alters the date format to use (I feel this is a big clue but not sure what to look for?)