Attribut lang in em label doesn't work

Hi,

In wordpress multisite i use the lang attribute in a em label for somme accesibility, but when i open with navigator the lang attribute disappears and i must use a <span> with the lang attribute like this

<span lang=”en”>< em>Hello world!</ em></span>

Someone knows how can i fix this to use only

<em lang=”en”>Hello world!</ em >

Thanks!