Improve locale directory detection

Use in-place locale directory if that exists, and
static one (RUN_IN_PLACE or CUSTOM_LOCALEDIR) doesn't exist.
Report to errorstream if neither static nor in-place locale
dirs exist, and report successfully found paths to infostreem.

Fixes two bugs:

-> Regression of commit [1] where if we use RUN_IN_PLACE=false,
	but don't make install, locales aren't found. One might
	think this is no regression, as its no bug, but all other
	paths (mainmenu, etc.) are detected properly.
-> Regression of commit [1] where locales don't work on windows.

References:
[1]: Commit 645e2086 "Use CUSTOM_LOCALEDIR if specified" by @ShadowNinja