code: func (r Resources) MergeByLanguage(r2 Resources) Resources {
  	result := append(Resources(nil), r...)
  	m := make(map[string]bool)
  	for _, rr := range r {
  		if translated, ok := rr.(translatedResource); ok {
  			m[translated.TranslationKey()] = true
  		}
  	}
  
  	for _, rr := range r2 {
  		if translated, ok := rr.(translatedResource); ok {
  			if _, found := m[translated.TranslationKey()]; !found {
  				result = append(result, rr)
  			}
  		}
  	}
  	return result
  }
docs: // MergeByLanguage adds missing translations in r1 from r2.