Copied from add_filter to generate WHERES for translation fields.

def add_filter(self, filter_expr, connector=AND, negate=False, trim=False,
            can_reuse=None, process_extras=True, force_having=False):
        """
        Copied from add_filter to generate WHERES for translation fields.
        """
        if force_having:
            import warnings
            warnings.warn("multilingual-ng doesn't support force_having (see Django ticket #11293)")
        arg, value = filter_expr
        parts = arg.split(LOOKUP_SEP)
        if not parts:
            raise FieldError("Cannot parse keyword query %r" % arg)

        # Work out the lookup type and remove it from 'parts', if necessary.
        if len(parts) == 1 or parts[-1] not in self.query_terms:
            lookup_type = 'exact'
        else:
            lookup_type = parts.pop()

        # Interpret '__exact=None' as the sql 'is NULL'; otherwise, reject all
        # uses of None as a query value.
        if value is None:
            if lookup_type != 'exact':
                raise ValueError("Cannot use None as a query value")
            lookup_type = 'isnull'
            value = True
        elif (value == '' and lookup_type == 'exact' and
              self.get_compiler(DEFAULT_DB_ALIAS).connection.features.interprets_empty_strings_as_nulls):
            lookup_type = 'isnull'
            value = True
        elif callable(value):
            value = value()

        opts = self.get_meta()
        alias = self.get_initial_alias()
        allow_many = trim or not negate

        try:
            field, target, opts, join_list, last, extra_filters = self.setup_joins(
                    parts, opts, alias, True, allow_many, can_reuse=can_reuse,
                    negate=negate, process_extras=process_extras)
        except MultiJoin, e:
            self.split_exclude(filter_expr, LOOKUP_SEP.join(parts[:e.level]),
                    can_reuse)
            return

        #=======================================================================
        # Django Mulitlingual NG Specific Code START
        #=======================================================================
        if hasattr(opts, 'translation_model'):
            field_name = parts[-1]
            if field_name == 'pk':
                field_name = opts.pk.name
            translation_opts = opts.translation_model._meta
            if field_name in translation_opts.translated_fields.keys():
                field, model, direct, m2m = opts.get_field_by_name(field_name)
                if model == opts.translation_model:
                    language_code = translation_opts.translated_fields[field_name][1]
                    if language_code is None:
                        language_code = get_default_language()
                    master_table_name = opts.db_table
                    trans_table_alias = get_translation_table_alias(
                        model._meta.db_table, language_code)
                    new_table = (master_table_name + "__" + trans_table_alias)
                    self.where.add(constraint_tuple(new_table, field.column, field, lookup_type, value), connector)
                    return
        #=======================================================================
        # Django Mulitlingual NG Specific Code END
        #=======================================================================
        final = len(join_list)
        penultimate = last.pop()
        if penultimate == final:
            penultimate = last.pop()
        if trim and len(join_list) > 1:
            extra = join_list[penultimate:]
            join_list = join_list[:penultimate]
            final = penultimate
            penultimate = last.pop()
            col = self.alias_map[extra[0]][LHS_JOIN_COL]
            for alias in extra:
                self.unref_alias(alias)
        else:
            col = target.column
        alias = join_list[-1]

        while final > 1:
            # An optimization: if the final join is against the same column as
            # we are comparing against, we can go back one step in the join
            # chain and compare against the lhs of the join instead (and then
            # repeat the optimization). The result, potentially, involves less
            # table joins.
            join = self.alias_map[alias]
            if col != join[RHS_JOIN_COL]:
                break
            self.unref_alias(alias)
            alias = join[LHS_ALIAS]
            col = join[LHS_JOIN_COL]
            join_list = join_list[:-1]
            final -= 1
            if final == penultimate:
                penultimate = last.pop()

        if (lookup_type == 'isnull' and value is True and not negate and
                final > 1):
            # If the comparison is against NULL, we need to use a left outer
            # join when connecting to the previous model. We make that
            # adjustment here. We don't do this unless needed as it's less
            # efficient at the database level.
            self.promote_alias(join_list[penultimate])

        if connector == OR:
            # Some joins may need to be promoted when adding a new filter to a
            # disjunction. We walk the list of new joins and where it diverges
            # from any previous joins (ref count is 1 in the table list), we
            # make the new additions (and any existing ones not used in the new
            # join list) an outer join.
            join_it = iter(join_list)
            table_it = iter(self.tables)
            join_it.next(), table_it.next()
            table_promote = False
            join_promote = False
            for join in join_it:
                table = table_it.next()
                if join == table and self.alias_refcount[join] > 1:
                    continue
                join_promote = self.promote_alias(join)
                if table != join:
                    table_promote = self.promote_alias(table)
                break
            self.promote_alias_chain(join_it, join_promote)
            self.promote_alias_chain(table_it, table_promote)

        self.where.add(constraint_tuple(alias, col, field, lookup_type, value), connector)

        if negate:
            self.promote_alias_chain(join_list)
            if lookup_type != 'isnull':
                if final > 1:
                    for alias in join_list:
                        if self.alias_map[alias][JOIN_TYPE] == self.LOUTER:
                            j_col = self.alias_map[alias][RHS_JOIN_COL]
                            entry = self.where_class()
                            entry.add(constraint_tuple(alias, j_col, None, 'isnull', True), AND)
                            entry.negate()
                            self.where.add(entry, AND)
                            break
                elif not (lookup_type == 'in' and not value) and field.null:
                    # Leaky abstraction artifact: We have to specifically
                    # exclude the "foo__in=[]" case from this handling, because
                    # it's short-circuited in the Where class.
                    entry = self.where_class()
                    entry.add(constraint_tuple(alias, col, None, 'isnull', True), AND)
                    entry.negate()
                    self.where.add(entry, AND)

        if can_reuse is not None:
            can_reuse.update(join_list)
        if process_extras:
            for filter in extra_filters:
                self.add_filter(filter, negate=negate, can_reuse=can_reuse,
                        process_extras=False)