fun readLangFiles(langFileDir: File, baseLang: String): Map<String, Map<MsgId, MsgStr>>
Reads all *.lang files in a directory into a map from the name of each language to a map that associates the string in the base language with the string translated to the current language.
langFileDir - the directory containing the *.lang files
baseLang - the base language from which the translators will translate to other languages