Added Directory.Build.targets, this seems to help to import the target correctly. Removed chocolatey package again, as this seems to be the more stable approach (let's see if the build runs...)

GreenshotConfluencePlugin/Support/ITranslationProvider.cs

@@ -1,4 +1,4 @@
-namespace TranslationByMarkupExtension {
+namespace GreenshotConfluencePlugin.Support {
     public interface ITranslationProvider {
         /// <summary>
         /// Translates the specified key.

GreenshotConfluencePlugin/Support/LanguageChangedEventManager.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Windows;
 
-namespace TranslationByMarkupExtension
+namespace GreenshotConfluencePlugin.Support
 {
     public class LanguageChangedEventManager : WeakEventManager
     {

GreenshotConfluencePlugin/Support/LanguageXMLTranslationProvider.cs

@@ -1,6 +1,6 @@
 using GreenshotPlugin.Core;
 
-namespace TranslationByMarkupExtension {
+namespace GreenshotConfluencePlugin.Support {
 	/// <summary>
 	/// 
 	/// </summary>

GreenshotConfluencePlugin/Support/TranslateExtension.cs

@@ -2,7 +2,7 @@
 using System.Windows.Data;
 using System.Windows.Markup;
 
-namespace TranslationByMarkupExtension
+namespace GreenshotConfluencePlugin.Support
 {
     /// <summary>
     /// The Translate Markup extension returns a binding to a TranslationData

GreenshotConfluencePlugin/Support/TranslationData.cs

@@ -2,7 +2,7 @@
 using System.ComponentModel;
 using System.Windows;
 
-namespace TranslationByMarkupExtension {
+namespace GreenshotConfluencePlugin.Support {
 	public class TranslationData : IWeakEventListener, INotifyPropertyChanged {
         private readonly string _key;
 

GreenshotConfluencePlugin/Support/TranslationManager.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace TranslationByMarkupExtension {
+namespace GreenshotConfluencePlugin.Support {
 	public class TranslationManager {
 		private static TranslationManager _translationManager;