diff --git a/frontend/apps/reader/modules/readerwikipedia.lua b/frontend/apps/reader/modules/readerwikipedia.lua
index 17821e181..34537ad33 100644
--- a/frontend/apps/reader/modules/readerwikipedia.lua
+++ b/frontend/apps/reader/modules/readerwikipedia.lua
@@ -1,5 +1,6 @@
 local ReaderDictionary = require("apps/reader/modules/readerdictionary")
 local EventListener = require("ui/widget/eventlistener")
+local NetworkMgr = require("ui/networkmgr")
 local Translator = require("ui/translator")
 local Wikipedia = require("ui/wikipedia")
 local UIManager = require("ui/uimanager")
@@ -17,7 +18,12 @@ local ReaderWikipedia = ReaderDictionary:new{
 }
 
 function ReaderWikipedia:onLookupWikipedia(word, box)
-    local lang = Translator:detect(word) or "en"
+    local ok, lang = pcall(Translator.detect, Translator, word)
+    -- prompt users to turn on Wifi if network is unreachable
+    if not ok and lang and lang:find("Network is unreachable") then
+        NetworkMgr:promptWifiOn()
+        return
+    end
     -- convert "zh-CN" and "zh-TW" to "zh"
     lang = lang:match("(.*)-") or lang
     local results = {}
diff --git a/frontend/ui/otamanager.lua b/frontend/ui/otamanager.lua
index 663b1130b..ac682f257 100644
--- a/frontend/ui/otamanager.lua
+++ b/frontend/ui/otamanager.lua
@@ -1,5 +1,6 @@
 local InfoMessage = require("ui/widget/infomessage")
 local ConfirmBox = require("ui/widget/confirmbox")
+local NetworkMgr = require("ui/networkmgr")
 local UIManager = require("ui/uimanager")
 local Device = require("ui/device")
 local DEBUG = require("dbg")
@@ -63,8 +64,13 @@ function OTAManager:checkUpdate()
     local r, c, h = http.request{
         url = ota_zsync_file,
         sink = ltn12.sink.file(io.open(local_zsync_file, "w"))}
-    -- parse OTA package version
+    -- prompt users to turn on Wifi if network is unreachable
+    if h == nil then
+        NetworkMgr:promptWifiOn()
+        return
+    end
     if c ~= 200 then return end
+    -- parse OTA package version
     local ota_package = nil
     local zsync = io.open(local_zsync_file, "r")
     if zsync then
diff --git a/frontend/ui/translator.lua b/frontend/ui/translator.lua
index 357d8c83b..13299d438 100644
--- a/frontend/ui/translator.lua
+++ b/frontend/ui/translator.lua
@@ -79,6 +79,8 @@ function Translator:detect(text)
         local src_lang = result.src
         DEBUG("detected language:", src_lang)
         return src_lang
+    else
+        return self.default_lang
     end
 end