Otherwise different strings from different projects can share same cache
entry (checksum is not enough as monolingual files base checksum only on
message identifier, which can be same for different strings).

Currently translated at 100.0% (819 of 819)

Currently translated at 100.0% (819 of 819)

Currently translated at 100.0% (819 of 819)

Currently translated at 100.0% (819 of 819)

Currently translated at 100.0% (819 of 819)

Currently translated at 100.0% (819 of 819)

Currently translated at 100.0% (819 of 819)

This way there is more clear there are some of them (issue #299).

Change OSX Strings to monolingual

The backend does not have to be saved for changing the flag as we track
it only internally.

Fixes #300

Currently translated at 92.6% (756 of 816)

This currently fails on monolingual files (issue #300)