lang::util::localize is executed on my site(s) running oacs-5-1 on every variable, yielding interesting results:
a) If a variable value starts with "-", the page breaks, as this value is treated as a switch to lang::util::localize (totally screwing up project-manager, as Jade made heavy use of it like in "--no customer--").
b) If you use Spell Checking, the variables returned from aspell are treated as "message keys" and are considered missing.
c) Even the documentation on lang::util::localize is not correctly displayed as it reads in the first sentence "Takes a string with embedded message keys on the format MESSAGE KEY MISSING: 'message_key_name' and returns the same string".
I have the distinct feeling that something during the last upgrade process went wrong, but I can't point my finger to it and I seriously hope anyone can shed some light on it.
I'm not posting this as a bug, as I assume this is a local problem and not a general one with the toolkit (as people would have screamed up otherwise).