With reference to: https://moodle.org/mod/forum/discuss.php?d=328567 it looks like it is possible for the non-language string 'thisdirection' to be translated. This is used in '/lib/pagelib.php':
which when translated can cause this in the More theme:
thus completely breaking it.
Therefore a 'guard' needs to be put in place to prevent this string from changing in the language pack.
Also noticed that 'btt' for 'thisdirectionvertical':
was also translated. This affects the dock.