Standardize directory/folder to folder (#7410)

Follow-up to https://github.com/koreader/koreader/pull/7328

frontend/apps/cloudstorage/dropboxapi.lua

@@ -128,7 +128,7 @@ function DropBoxApi:listFolder(path, token, folder_mode)
     -- Add special folder.
     if folder_mode then
         table.insert(dropbox_list, 1, {
-            text = _("Long-press to select current directory"),
+            text = _("Long-press to select current folder"),
             url = path,
             type = "folder_long_press",
         })

frontend/ui/screensaver.lua

@@ -203,7 +203,7 @@ function Screensaver:chooseFolder()
                         logger.dbg("set screensaver directory to", path)
                         G_reader_settings:saveSetting("screensaver_dir", path)
                         UIManager:show(InfoMessage:new{
-                            text = T(_("Screensaver directory set to:\n%1"), BD.dirpath(path)),
+                            text = T(_("Screensaver folder set to:\n%1"), BD.dirpath(path)),
                             timeout = 3,
                         })
                     end,

frontend/ui/widget/dictquicklookup.lua

@@ -367,7 +367,7 @@ function DictQuickLookup:init()
                                            or require("apps/filemanager/filemanagerutil").getDefaultDir() end
                         if not dir or not util.pathExists(dir) then
                             UIManager:show(InfoMessage:new{
-                                text = _("No directory to save article to could be found."),
+                                text = _("No folder to save article to could be found."),
                             })
                             return
                         end

plugins/coverimage.koplugin/main.lua

@@ -27,7 +27,7 @@ local function pathOk(filename)
     elseif name == "" then
         return false, _("Please enter a filename at the end of the path.")
     elseif lfs.attributes(filename, "mode") == "directory" then
-        return false, T(_("The path \"%1\" must point to a file, but it points to a directory."), filename)
+        return false, T(_("The path \"%1\" must point to a file, but it points to a folder."), filename)
     end
 
     return true