Bootstrap allows to translate/change the label of the upload button of acustom-file input via SCSS, seeBootstrap docs:

$custom-file-text: (en:"Browse",es:"Elegir");

This works by generating the following CSS which depends on thelang attribute of the input:

.custom-file-input:lang(es)~ .custom-file-label::after {content:"Elegir";}

This however currently does not work with the HTML generated by the theme since the resulting HTML is of the form (redacted here to the relevant parts):

<divclass="custom-file"><inputtype="file"id="..."class="custom-file-input"><labelfor="..."lang="es"class="custom-file-label"></label></div>

while it should be of the form

<divclass="custom-file"><inputtype="file"id="..."lang="es"class="custom-file-input"><labelfor="..."class="custom-file-label"></label></div>

i.e. thelang was placed on thelabel instead of theinput.

This PR fixes this to be compatible with Bootstrap 4.