.lang-btn {
  background: none;
  border: 1px solid rgba(255, 255, 255, 0.4);
  color: rgba(255, 255, 255, 0.7);
  border-radius: 4px;
  padding: 2px 10px;
  font-size: 0.8rem;
  cursor: pointer;
  margin-left: 4px;
  text-decoration: none;
  display: inline-block;
}
.lang-btn.active,
.lang-btn:hover {
  border-color: #fff;
  color: #fff;
  background: rgba(255, 255, 255, 0.15);
}

.wrapper{
    min-height: 100vh;
    position: relative;/*←相対位置*/
    padding-bottom: 120px;/*←footerの高さ*/
    box-sizing: border-box;/*←全て含めてmin-height:100vhに*/
}

footer{
    width: 100%;
    background-color: #89c7de;
    color: #000;
    text-align: center;
    padding: 30px 0;

 position: absolute;/*←絶対位置*/
    bottom: 0; /*下に固定*/
}