NAME_FORMAT = /^(?!.*.S)[a-zA-Z àâäôéèëêïîçùûüÿæœÀÂÄÔÉÈËÊÏΟÇÙÛÜÆŒößÖẞąćęłńóśźżĄĆĘŁŃÓŚŹŻìíòúÌÍÒÚáñÁÑ ',.-]+$/

  validate :name_is_acceptable, if: -> { (last_name_changed? || first_name_changed?) && (persisted? || !imported?) }
  def name_is_acceptable
    [:first_name, :last_name].each do |attr|
      value = self.send(attr)
      next if value.blank? || value =~ NAME_FORMAT

      errors.add attr, I18n.t(:resident_name_invalid, scope: 'errors.messages')
    end
  end

<%= text_field_tag 'resident[last_name]', nil, class: 'form-control', placeholder: 'Last Name', required: true, maxlength: 50, pattern: '^(?!.*.S)[a-zA-Z àâäôéèëêïîçùûüÿæœÀÂÄÔÉÈËÊÏΟÇÙÛÜÆŒößÖẞąćęłńóśźżĄĆĘŁŃÓŚŹŻìíòúÌÍÒÚáñÁÑ ',.-]+$', oninvalid: "setCustomValidity('Contains unsupported characters.')", oninput: "setCustomValidity('')" %>

Pattern attribute value (?-mix:^(?!.*.S)[a-zA-Z àâäôéèëêïîçùûüÿæœÀÂÄÔÉÈËÊÏΟÇÙÛÜÆŒößÖẞąćęłńóśźżĄĆĘŁŃÓŚŹŻìíòúÌÍÒÚáñÁÑ ',.-]+$) is not a valid regular expression: Uncaught SyntaxError: Invalid regular expression: /(?-mix:^(?!.*.S)[a-zA-Z àâäôéèëêïîçùûüÿæœÀÂÄÔÉÈËÊÏΟÇÙÛÜÆŒößÖẞąćęłńóśźżĄĆĘŁŃÓŚŹŻìíòúÌÍÒÚáñÁÑ ',.-]+$)/: Invalid group