I created a phab task to track this known work that needs to happen soon.
|Resolved||ssastry||T229015 Tracking: Direct live production traffic at Parsoid/PHP|
|Open||cscott||T237436 Fix load times for language variant FST files|
This should be mostly addressed by I58d54dec51e8a4da0d1f0ba68144a2dd0cac6235 / 9d17caeca8310a748c956a6c3f8efbf3c9073d49 in the langconv library. That still does a file_get_contents() to load the FST; we could compile these into PHP files with a string constant to allow caching the data across PHP instances. Waiting for initial performance metrics to determine if that additional step is necessary (or effective: it may be that APC refuses to cache such large class files).