Searching for a single instance of a value in a string

So I’ve set up a custom meta value for a plugin WordPress Job Manager however I think any one knowledgeable in WordPress / PHP could help me.

The field I set up is for language and it works well when only 1 language is entered into the field however the dropdown menu I set up to search for languages can’t handle it when any more then one language is entered into it.

The drop down is set up like this :

add_action( 'job_manager_job_filters_search_jobs_end', 'filter_by_language_field' );
function filter_by_language_field() {
  ?>
  <div class="search_language">
    <label for="search_language"><?php _e( 'Language', 'wp-job-manager' ); ?></label>
    <select name="filter_by_language" class="job-manager-filter">
     <option value="">All languages</option>
     <option value="french"><?php _e( 'French', 'wp-job-manager' ); ?></option>
</select>
  </div>
  <?php
}
/**
 * This code gets your posted field and modifies the job search query
 */
add_filter( 'job_manager_get_listings', 'filter_by_language_field_query_args', 10, 2 );
function filter_by_language_field_query_args( $query_args, $args ) {
  if ( isset( $_POST['form_data'] ) ) {
    parse_str( $_POST['form_data'], $form_data );
    // If this is set, we are filtering by salary
    if ( ! empty( $form_data['filter_by_language'] ) ) {
      $selected_range = esc_html( $form_data['filter_by_language'] );
      switch ( $selected_range ) {
        case 'french' :
          $query_args['meta_query'][] = array(
            'key'     => '_job_language',
            'value'   => 'French',
            'compare' => '=',
            'type'    => 'CHAR'
          );
        break;
      }      
      // This will show the 'reset' link
      add_filter( 'job_manager_get_listings_custom_filter', '__return_true' );
    }
  }
  return $query_args;
}

So as I said earlier this format works great for when a single language is entered into the custom field e.g. French however if multple are entered in e.g. French, German, Italian, Polish, Spanish it wont detect that french is there.

I’ve tried using various compare operators but can’t seem to get it quite right.

Any help is appreciated