Add support of collation when ordering translatable fields
It will be good to use the collation [1] of the current language when ordering a translatable field. It could be added in 'FieldTranslate.convert_order'.
Of course it will require first to implement it in python-sql [2].
Wrong collation when sorting column can be performance killing. We just discover that for a column filled in Lao and with a default collation of 'en_US', the performance of a query ordering on this column is very poor. By switching to 'C', we got a speed improvement of a factor of 1000 for about 1000 tuples.
Of course, this feature will not fix untranslatable field with bad database default collation.
[1] https://www.postgresql.org/docs/current/static/collation.html
[2] https://python-sql.tryton.org/bug51