Load a tt file's tt dict into |self.tt_dd|.
        |tt| means text transform.
        
        locale: locale key into |self.tt_dd|.
        path_func: tt file path func
        encoding: tt file encoding

def load_tt_file(self, locale, path_func=None, encoding=None):
        """
        Load a tt file's tt dict into |self.tt_dd|.
        |tt| means text transform.
        
        locale: locale key into |self.tt_dd|.
        path_func: tt file path func
        encoding: tt file encoding
        """
        
        #/
        path_func = path_func or self.path_func
        
        encoding = encoding or self.file_encoding
        
        #/ get path
        path = path_func(locale)
        
        #/ load dict from locale file
        tt_file_d = yaml.load(codecs.open(path, mode='r', encoding=encoding))
        
        #/
        target_locale = tt_file_d.get(I18n.TT_FILE_K_SYNONYM, None)
        
        #/ if the locale file is in synonym format
        ## Y
        if target_locale:
            #/ load the target locale file instead
            return self.load_tt_file(locale=target_locale, path_func=path_func, encoding=encoding)
        ## N
        
        #/ get the tt dict from the file dict
        tt_d = tt_file_d[I18n.TT_FILE_K_TT]
        
        #/ add to 
        self.load_tt_dict(locale=locale, tt_d=tt_d)
        
        #/ return the true locale
        ## this is useful in case the original locale file is in synonym format
        return locale