[https://github.com/tracim/tracim/issues/809] added lang label on header

frontend/src/component/Header/MenuActionListItem/DropdownLang.jsx

 require('./DropdownLang.styl')
 
 const DropdownLang = props => {
+  const activeLang = props.langList.find(l => l.id === props.idLangActive)
   return (
     <li className='header__menu__rightside__itemlanguage'>
       <div className='header__menu__rightside__itemlanguage__languagedropdown dropdown'>
           aria-haspopup='true'
           aria-expanded='false'
         >
-          <img className='languagedropdown__btnlanguage__imgselected' src={props.langList.find(l => l.id === props.idLangActive).icon} />
+          <img className='languagedropdown__btnlanguage__imgselected' src={activeLang.icon} />
+          { activeLang.label }
         </button>
         <div className='languagedropdown__subdropdown dropdown-menu' aria-labelledby='headerDropdownMenuButton'>
           { props.langList.filter(l => l.id !== props.idLangActive).map(l =>

frontend/src/component/Header/MenuActionListItem/DropdownLang.styl

       margin-right 10px
       width 20px
       height 15px
+      vertical-align middle
   &__subdropdown
     padding 0
     min-width 0