fix current language detection (#166, #169)

Author: fritzmg

page/layouts/partials/menu.html

@@ -48,8 +48,9 @@ <h3>{{ if not $disableShortcutsTitle}}{{ T "Shortcuts-Title"}}{{ end }}</h3>
             <i class="fas fa-language fa-fw"></i>
           <div class="select-style">
             <select id="select-language" onchange="location = this.value;">
+              {{ $pageLang := .Page.Lang }}
               {{ range .AllTranslations }}
-                {{ if eq .Page.Lang .Lang }}
+                {{ if eq $pageLang .Lang }}
                   <option id="{{ .Language }}" value="{{ .Permalink }}" selected>{{ .Language.LanguageName }}</option>
                 {{ else }}
                   <option id="{{ .Language }}" value="{{ .Permalink }}">{{ .Language.LanguageName }}</option>