I can't clarify further, since i have never seen the problem on any site, and there is no way to reproduce the problem without more information. My explanation was based on the source code of lang::util::translator_mode_p [1] and ad_get_client_property [2]. Since "-cache-only" was not set in the call, and - as you said - you are not using a secure connection, the only option is that the empty value was coming from the database. ... but i have no idea, how it got there. Maybe related to your modifications?
-g
[1] https://openacs.org/api-doc/proc-view?proc=lang%3a%3autil%3a%3atranslator_mode_p&source_p=1
[2] https://openacs.org/api-doc/proc-view?proc=ad_get_client_property&source_p=1
