Hi,
You have to add more languages at /apps/wcm/core/resources/languages.
OOTB languages for tagging populate from the/libs/wcm/core/resources/languages node; you override the /libs/wcm/core/resources/languages node and add only additional languages at /apps/wcm/core/resources/languages similar to the languages in libs.
the logic is at /libs/cq/tagging/gui/components/tagedit/languagepicker/render.jsp
Arun Patidar