[misc] Fix preference language mock

xwiki-platform-core/xwiki-platform-oldcore/src/test/java/com/xpn/xwiki/test/MockitoOldcoreRule.java

@@ -371,8 +371,6 @@ && getMocker().getInstance(Environment.class) instanceof ServletEnvironment) {
 
         // XWiki
 
-        doReturn("en").when(getSpyXWiki()).getLanguagePreference(anyXWikiContext());
-
         doAnswer(new Answer<XWikiDocument>()
         {
             @Override
@@ -583,6 +581,8 @@ public String answer(InvocationOnMock invocation) throws Throwable
             }
         }).when(getSpyXWiki()).getLanguagePreference(anyXWikiContext());
 
+        getXWikiContext().setLocale(Locale.ENGLISH);
+
         // XWikiStoreInterface
 
         when(getMockStore().getTranslationList(anyXWikiDocument(), anyXWikiContext())).then(new Answer<List<String>>()