Код:
<html>
<head>
<style>
.field { padding:2px 2px; border:1px solid #aaa; box-shadow:inset 2px -2px 5px #aaa; border-radius:5px; width:200px; height:40px; }
</style>
<script>
var lang = 'ru';
function i18n(str_lang) {
  var el_c = [].slice.call(document.body.children);
  el_c.forEach(item => { 
    var str_tr = item.getAttribute('data-' + str_lang);
      if(str_tr) {
        if(item.tagName != 'INPUT')
          item.innerHTML = str_tr;
        else {
          item.value = str_tr;
          item.onclick = function() { this.value = ''; }
        }
      }
  });
}

window.onload = function() {
  i18n(lang);
}

function _i18n() { i18n(lang); }

</script>
</head>
<body onclick="_i18n();">
  <input class="field" data-en="value" data-de="Wert" data-ru="значение" value="">
  <br>
  <p data-en="Firstname:" data-de="Vorname:" data-ru="Имя:">Firstname</p>
  <div data-en="Lastname:" data-de="Nachname:" data-ru="Фамилия:">Lastname</div>
  <br>
  <a href="javascript:lang='en';i18n('en');">En</a>&nbsp;&nbsp;
  <a href="javascript:lang='de';i18n('de');">De</a>&nbsp;&nbsp;
  <a href="javascript:lang='ru';i18n('ru');">Ru</a>&nbsp;&nbsp;
</body>