Revert "Don't store localisation cache in DB, it creates too much debug log noise"

When redis is being used for other things (task queue, etc) it can run out
of memory and start evicting things. When it evicts l10n cache, it makes
the wiki sad.

This reverts commit 021cd27b949fb1567403bbc5b0fe8a1f0e30a482.

Change-Id: I18d5d32cefa7bb2c5e9a0a99af109b731d0277e8
Merge "Revert "Don't store localisation cache in DB, it creates too much debug log noise""