Add some title.

Author: pawchen

converter/templates/Partials/de/DocHeader.cshtml

@@ -2,7 +2,8 @@
 
 <div class="col-sm-6">
     <div class="btn-group">
-        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
+        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"
+                title="Choose language - Sprache auswählen - 言語を選択 - 选择语言">
             Deutsch <span class="caret"></span>
         </button>
         <ul class="dropdown-menu">

converter/templates/Partials/en/DocHeader.cshtml

@@ -2,7 +2,8 @@
 
 <div class="col-sm-6">
     <div class="btn-group">
-        <button disabled="@(Model.AvailableLanguages.Length < 2)" type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
+        <button disabled="@(Model.AvailableLanguages.Length < 2)" type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"
+                title="Choose language - Sprache auswählen - 言語を選択 - 选择语言">
             English <span class="caret"></span>
         </button>
         <ul class="dropdown-menu">

converter/templates/Partials/ja/DocHeader.cshtml

@@ -2,7 +2,8 @@
 
 <div class="col-sm-6">
     <div class="btn-group">
-        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
+        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"
+                title="Choose language - Sprache auswählen - 言語を選択 - 选择语言">
             日本語 <span class="caret"></span>
         </button>
         <ul class="dropdown-menu">

converter/templates/Partials/zh/DocHeader.cshtml

@@ -2,7 +2,8 @@
 
 <div class="col-sm-6">
     <div class="btn-group">
-        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
+        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"
+                title="Choose language - Sprache auswählen - 言語を選択 - 选择语言">
             简体中文 <span class="caret"></span>
         </button>
         <ul class="dropdown-menu">