Improving check for which tinymce lang to use (Bug #1319302)

In tinymce 4 some lang packs are written lower_UPPER.js
eg for french it is fr_FR.js so we need to detect for this possibility
as well.

Change-Id: I8c813d4f9b4b888940203b3180a03c9995c542ee
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Merge "Improving check for which tinymce lang to use (Bug #1319302)"