How to make language choice Required for Taxonomy term
Write a custom module and use the following code

function MYMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id){
  if($form_id=='taxonomy_form_term'){
     $form['#after_build'][] = 'MYMODULE_after_build';
  }
}

function MYMODULE_after_build($form, &amp;$form_state) {
   if($form['language']['#value']=='und'){
     $form['language']['#default_value']='en';
     $form['language']['#value']='en';
   }
   return $form;


}

NOTE: In your custom_module.info file use this dependencies[] = i18n_taxonomy, so that your module can only be enabled if internationalization is enabled