.langChangeButton{
  display: none;
}
.langChangeButton:checked + label{
  background-color: skyblue;
}
label{
  display: inline-block;
  border: 1px solid #000;
  padding: 2px 2px;
  width: 55px;
  height: 25px;
  text-align: center;
}
#langJa:not(:checked) ~ :lang(ja){
  display: none;
}
#langEn:not(:checked) ~ :lang(en){
  display: none;
}