Sitecore Backend Labels missing

Question

I have a Sitecore 7.5 instance, where the backend is broken after installing some packages with content, layouts and templates from an old Sitecore 6.3 SIP 3.2 instance and the new built DLLs from the solution. I also merged the config files of both instances.

This is how the backend of the 7.5 instance looks now:

Any idea what causes this and how I can fix this?

Thanks in advance!

EDIT: Labels and Save issue fixed. Getting an error message on the website.

Frontend error message:

[InvalidOperationException: intranetContext]
   Sitecore.Diagnostics.Assert.IsNotNull(Object value, String message) +55
   Sitecore.Intranet.Utils.IntranetUtil.get_CurrentIntranetSite() +403
   Sitecore.Intranet.Settings.IntranetSettings.get_SiteDatabase() +89
   Sitecore.Intranet.Utils.IntranetLanguageResolver.get_LanguageList() +61
   Sitecore.Intranet.Utils.IntranetLanguageResolver.get_FullLanguageList() +188
   Sitecore.Intranet.Utils.IntranetLanguageResolver.GetLanguageList(Boolean isContentArea, Boolean isExclusiveQS) +149
   Sitecore.Intranet.Utils.IntranetLanguageResolver.GetLanguage(Item item, Boolean isContentArea, Boolean isExclusiveQS) +74
   Sitecore.Intranet.Utils.IntranetLanguageResolver.IsContentLanguageAccessible(Item item, Language& language) +135
   Sitecore.Intranet.HtmlControls.LocalizedPlaceholder.EnterContentArea() +81
   Sitecore.Intranet.HtmlControls.LocalizedPlaceholder.OnInit(EventArgs e) +46
   System.Web.UI.Control.InitRecursive(Control namingContainer) +186
   System.Web.UI.Control.InitRecursive(Control namingContainer) +291
   System.Web.UI.Control.InitRecursive(Control namingContainer) +291
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2098