<div class="lang_switch">
   <div class="lang_switch__text pl">PL</div>
   <div class="lang_switch__text en">EN</div>
   <div class="lang_switch__blobs"></div>
</div>

<svg xmlns="http://www.w3.org/2000/svg" version="1.1" style="display: none">
   <defs>
      <filter id="goo">
         <feGaussianBlur in="SourceGraphic" stdDeviation="10" result="blur" />
         <feColorMatrix in="blur" mode="matrix" values="1 0 0 0 0  0 1 0 0 0  0 0 1 0 0  0 0 0 18 -7" result="goo" />
         <feBlend in="SourceGraphic" in2="goo" />
      </filter>
   </defs>
</svg>

* {
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
*,*::before,*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  height: 100vh;
  display: flex;
  font-size: 30px;
  font-family: "Roboto", sans-serif;
  font-weight: 700;
  color: #121212;
  background-color: #2d9cdb;
}

$padding: 10px;
$margin: 5px;
$width: 80px;

.lang_switch {
  position: relative;
  display: flex;
  margin: auto;
  padding: $padding;

  &__text {
    width: $width;
    height: $width;
    line-height: $width;
    text-align: center;

    &:first-of-type {
      margin-right: $margin;
    }
  }
  &__blobs {
    position: absolute;
    z-index: -1;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    filter: url("#goo");

    &::before,
    &::after {
      content: "";
      position: absolute;
      z-index: -1;
      top: $padding;
      left: $padding;
      width: $width;
      height: $width;
      border-radius: 100%;
      background-color: #fefefe;
      transition: transform 0.2s cubic-bezier(0.51, 0.06, 0.56, 1.37);
      will-change: transform;
    }
    &::before {
      transform: scale(0.7);
      transition-delay: 0.1s;
      transition-duration: 0.4s;
    }
  }
}

.lang_switch.changed {
  .lang_switch__blobs {
    &::before {
      transform: translateX($width + $margin) scale(0.7);
    }
    &::after {
      transform: translateX($width + $margin);
    }
  }
}

// desktop
@media only screen and (min-width: 1025px) {
  .lang_switch__blobs::before {
    transform: scale(1);
    transition-delay: 0s;
    transition-duration: 0.2s;
  }
  .lang_switch:hover {
    cursor: pointer;
  }
  .lang_switch:not(.changed) {
    .en:hover ~ .lang_switch__blobs {
      &::before {
        transform: scale(0.9);
      }
      &::after {
        transform: translateX($width + $margin) scale(0.7);
      }
    }
  }
  .lang_switch.changed {
    .lang_switch__blobs::before {
      transform: translateX($width + $margin);
    }
    .pl:hover ~ .lang_switch__blobs {
      &::before {
        transform: translateX($width + $margin) scale(0.9);
      }
      &::after {
        transform: scale(0.7);
      }
    }
  }
}

const lang_switch = document.querySelector('.lang_switch');

lang_switch.onclick = () => lang_switch.classList.toggle('changed')